Feed with every water?

not in soil. Seeds are good for 2 weeks, then your soil may be good for uptp 2 months... depends on many variables. Stick to watering in small radius around the small plants and increase that radius as it grows... make sure it gets all the way through pot.. deep into it, not superficial. Wait for top 1" to dry and repeat. If you see the initial cotyledon leaves start to fade, maybe start with 1/4 strength every 1/3rd irrigation... build up from there, maybe every other when it is larger with a normal concentration (brands may be strong or not, takes trial and error, always read plant). get into a good rhythm / schedule as that makes adjusting easier, but when plant behaves differenlty, don't blindly follow any schedule. Any change that happens is likely our fault, so pay attention and catch things early -- even if it's working for other plants treated exactly the same. Autoflowers? so take it easy on them, they need less ferts in general.

I'd do something more like feed water water feed.. but it's really kind of up your plants.. they will tell you if they are suffering. underfeeding is often a better course of action the feeding too much. Too much is very hard to fix.. too little is easy to fix.