Give it 18/6 for the first 4-6 weeks, this will ensure it gets a good start and doesn't freak out at the weird 12/12 photoperiod.
Plants are easy to grow, they all need the same things - water, light and food.
I second the good choice comment, autos are disappointing and even more so for new growers.
Who wants to spend 3 months growing 15 grams?
Starting your seed at 12/12 will mean very slow going and the strange photoperiod could cause the plant to go hermaphrodite or do other strange things due to not having the correct/normal conditions. I have no idea who or why anybody would consider 12/12 as a good idea, it is just too weird for my brain to comprehend. The first few weeks of your plants life are so important and to torture your seedling by limiting its growth with only 12 hours of light is almost a joke in my opinion. Give it what it needs, a good dose of light so it can get established and growing properly, and if space is a problem, flipping to 12/12 at 4 weeks will still see manageable plants that will grow and flower normally, without any handicaps imposed by restricting its ability to grow from day one, which can/will play merry havoc with the plants hormones and confuse it no end.
Also, your seedling needs good root room to develop properly, so please, do not use cups of any sort!!!!
Something around 4 inches across and 5 inches deep will provide all it needs for the first 2-3 weeks of life.
Also, do not use a cover/humidity dome - it is not needed, your plant needs good air exchange to grow properly and some air movement to strengthen the stem. Living under a mini sweat lodge (dome) can cause moulds and fungus to attack, as well as risking cooking your plant due to the lack of air movement/exchange. Cannabis is not a rain forest plant and does not need artificially high humidity levels, ever, unless they are cuttings/clones without roots. Do not mist your seedlings, they do not need it - same mould/fungal problems as under a dome.
Also, also, make sure you buy the best light you can afford, lighting is where most people fall short,. Your plants need fantastic lighting to be able to grow fantastic flowers - something a cheap blurple light will never do.
Also, also also, deep watering every few days is better than shallow watering often. Your plants roots will be 2-3 times longer than the seedling is tall, so spritzing or syringe watering is totally inadequate! Water needs to get down deep. Wait until the top inch or so (maybe a bit less for seedlings, half inch or so) is dry before watering again. Aim for a moist substrate, not too wet and not too dry, just "Goldilocks" moist. And water from edge to edge of the pot too, roots need to be encouraged to grow wide and stabilize the plant, watering just next to the stem is again, totally inadequate.
Go easy on the feeding, it is better to give half strength more often than it is to give full strength infrequently. Especially when young, quarter strength is plenty and in early veg, half strength is plenty, leave full strength for when your plant is flowering and has a ravenous appetite.
Remember too, it is very easy to fix a slight under feeding, but very, very hard to rescue and save a badly burnt, over fed plant!
Also also, do not put too much perlite in your mix, 5-10% is more the suitable, it provides no nutrients and is only needed for drainage, something most modern mixes have plenty of anyhow.
And my biggest hint, do not under any circumstances defoliate your plants. Every healthy green leaf that gets removed just reduces the plants capacity to produce energy, thereby slowing growth. Cannabis has evolved to grow her biggest and best flowers, Getting rid of perfectly healthy green, energy producing leaves is not part of that process. Cannabis will grow its healthiest and fastest with every green leaf doing its job of making energy. Try to only remove yellow leaves, for by the time they are yellow, they have served their purpose. In 35+ years of growing, I have never seen a plant that gets rid of its own healthy green energy producing leaves for no purpose or benefit! Removing leaves to expose "potential bud sites" (branches really) is pointless, the branches will grow out from under the leaves in 3-5 days time anyhow, besides, those branches are relying on the energy produced by the big fan leaves so that they can grow, making leaf removal doubly pointless.
When it comes time to feeding your plants, try not to fall into the trap of buying everything in the shop. Look for a one bottle complete nutrient solution for growth and another for flowering. Add in a cal/mag supplement and a P/K booster for flowering, and this is all that is really needed. Another supplement I would add is a humic/fulvic and amino acid tonic, your plants will love it at all stages of its life, plus if you are growing in soil, a mycorrhizal supplement can work wonders and after a bit of experimenting, I can whole heartedly recommend "Mykos" from Xtreme Gardening, it is simply astounding the difference it and similar products, can have on plant health and nutritional absorption.
The reason I recommend "one bottle" grow and "one bottle" bloom nutrients, is as a first time grower you really don't want to be in a situation whereby the fertilizer is of such a type that you have to mix part A with part B, but not part C until week 34567, as this is just confusing. By using a complete one bottle nutrient, it will allow you to concentrate on the basics of watering, lighting intensity, air circulation etc and getting a feel for what is required by your plant for their happiest growth. If you are into organics, Bio Canna put out "Bio-Vega" and Bio-Flores", B.A.C. put out "Organic Grow" and "Organic Bloom" which are truly excellent products and GHE who put out "Flora Nova Grow" and "Flora Nova Bloom", which are also awesome. All these products are well and truly "one bottle wonders" that will do everything they claim and have been used by me for many years with outstanding results. They are also all highly concentrated, meaning very little is required, making each bottle quite economical, as they will last many, many plants or multiple grows.
And lastly, the biggest tip - write everything you do down! Start a dedicated diary for each pant and take notes about everything. Such things as when and what fertilizer and how much, germination times, growth rates, lighting schedules, temps, flowering speed, etc etc. I even make notes about seed descriptions! Having notes will be one of the best ways to improve your grows, noting what works and what doesn't will give you a base to start your next and subsequent grows on. Believe me, thinking you will remember is not going to cut it! Add a few months, some herbal inhalation and some other distractions, and what you thought you might remember, is lost forever! Also write it down as you do it, do not leave it to memory, as inevitably - was it 15 or 25 millilitres of nutrient A that I used and was it pH 6.5 or 5.6?? TRUST ME, do not chance things to memory!! With a diary for each plant, you will also have a self described "cheat sheet" to use next time you grow "Killer Strain 4XH87Z" and this can be invaluable to planning grows and plant requirements. Personally I stumbled through growing for 15 years and leaving everything to chance and memory, but once I started making diaries, results went ahead in leaps and bounds. I now have 20 odd years of notes regarding my grows and while I have settled on a few basic principles that work for me and in my situation, I still learn and discover new things each and every grow that I do. Without notes, it all becomes alphabet soup!
Hope this helps,..............
Organoman.
(well you did ask for any tips!)