Is this big enough to start in? Plus my first grow

Hey rollers! I had a quick question on a solo cup I have. Is it big enough to start a new grow in? And how does my 12 day old first grow look? She's under a 2700k 4200 lumen cfl. Im using black magic professional soil and it does run a lil hot as you can see. I hope the new seed I planted survives as long as the first. Im planning to get some organic soil soon as well as distilled water and ph strips. Any tips and advice is helpful thanks!

Yeah that's fine I always start my seedlings in tray/seedling pots roughly same size if not smaller