8 days is a long time, but it won't rot at that point. You get up to 10-14 days and it's probably failed to germ (you'll find an unopened seed) or it germed and failed to grow for one reason or another.
Depth is something you'll want to do a little trial and error with. Too long to sprout, go a bit shallower, but if you see seed shells stuck on the sprouts, you need to go slightly deeper.
A heat mat can improve consistency of how long it takes to sprout in any environment that is not warm naturally. A heat mat with a thermostat can be useful if the subsbtrate can maintain 76F on it's own. Substrates will always be a bit cooler than ambient temperatures due to evaporation occurring and assuming no other significant heat source involved.
There's nothing wrong with a humidity dome. Watering seeds that are germinating/not sprouted is a bad idea and should be avoided. A humidity dome can prolong that first re-irrigation well beyond expected sprout times. I'd rather do my 2nd irrigation when they have sprouted. Definitely take off the dome when they sprout.
Don't half-water. Always saturate entire pot. don't mist the top layer, don't add a 'capful' .. do it right and not some esoteric bro science nonsense. This is why i use the humidity dome. An unsprouted seedling is delicate. Avoid it because it is easily avoided and you never drown a seedling or cause rot, lol. Avoid the risk altogether. If normal watering habits cause a context of "too wet" that is the fault of soil constitution, lol. A self-inflicted problem in other words.
I get sprouts anwhere from 2-3 days on the fastest first wave, and stragglers might take up to 5 days, but that's quite rare. I used to have a much larger range of sprout times and fewer in the 2-3 day range before i used a heat mat. I live in a cold climate area. No paper towel. No soaking prior to planting in substrate. Simple, easy, concsistent results is the goal. Don't over-complicate it. *soaking may help with very old seeds... or not. i've only seen anecdotal testimonies on that.
1) water the pots. Don't compress the shit out of it. Keep it fluffy and airy. If perlite floats to top, you can stir it up and gently tamp down if your OCD requires it.
2) press down with finger in center mayabe 1/2" deep - this compresses a small amount of substrate for the seed to securely lie with no fear of sinking in further, and still fluffy all around it.
3) drop seed in and cover from sides loosely, and gently tamp down to make sure no light is getting in there and moisture is retained. Don't go overboard or it'll slow the sprout times.
I don't worry about seed orientation beyond avoiding it being upside down. If i lie it sideways i don't have to remember which side opens up, lol. Even an upside-down seed has a good chance of sprouting (a seed knows which way to grow on its own), but it can take longer or even get tangled on itself so it's just better to avoid it even if it is a low-risk thing.