Week 3- time to transplant and feed??

You're growing in soil that is likely already fertilized. From what I've seen browsing journals, the #1 killer of plants, and of poor yields and stunting for the survivors, is early feeding/over feeding, often worsened by over-watering. I didn't use any real nutes or add fertilizer and pulled just over an ounce from my first grow. Its more about what you feed it, and sticking to the "less is more" principal with soil as its likely already fertilized. You can add some things as early as week 1 if they have a 0-0-0 NPK rating or are close: things like a silica additive or rooting agent to promote better root aeration, and protection from disease. But seedlings are very sensitive so that's about it, or maybe certain organic additions, as the soil provides enough for at least the first 14 days. Some will give autoflowers a very weak taste of veg nutes on day 14: 1/8th-1/4 strength and no stronger in soil that early. By Day 21 from the day it popped up, you can increase to half strength but more will likely reward you only with nute burn as recommended doses are usually for photos in hydro; autos and anything in soil require less nutes and burn easier from over/early feeding. With nutes, less is more. If a little works, more will often cause harm instead of benefit.

when you do, bury them a bit so you shorten up that stem... provide stronger light ASAP to stop scary stretch. what you pot up to depends on what you want to do. A large pot and small plant is more difficult to water and fertilize optimally, but you can do it... and with autoflowers you want to keep transplanting to a minimum. in the case of an auto, i'd say a 3-gallon or 5-gallon is as large as you'll ever need. seeds are usually packed with enough power for first couple sets of real leaves. So, if it's been 2 weeks, i don't think a little feed is going to be a problem... runoff so it doesn't build up, etc... also assumes you don't have a 'hot' soil. soils often come with nutrients to start. too many variables to say exactly what you should or shouldn't do.

Q1 - better wait. These plants are very small and do not have developed rooting system. They drink too few water. If you put them in big pot, it will take ages to dry and you risk overwatering (happened to me) Q2 - better wait. Plan needs to develop roots first. Now you can easily burn them. If you use good soil (I use plagron royal mix) it has fertilizers for 6 weeks. Q3 - if they fell, then yes. Otherwise the stem will become stronger very soon. Small plants become tall (leggy) if they do not have enough light (weak lamp for indoor or far from light for outdoor). Good luck and feel free to DM in case of need!