4-Weekers Looking Poor.. Ideas?

[fordido]

I have only started from seed once before, but had lush & beautiful plants with no issues. I feel like they're looking a bit sad & puny this time around. I'd love any advice on what I could be doing better this year or next! I'm wondering if the issue might be tied to fertilizing, I can't remember if I skipped it last time..

Here's what I've so far this year:

• Started 3 seeds per cell in these starter kits using Light Warrior seed starting mix (https://www.gardeners.com/buy/deep-r.../35-657RS.html). Kept in the house with no drafts
• Germination was good & all seemed well for a while. I clipped off the extra seedlings at the soil line, leaving only the strongest one per cell.
• T5 Lights on for roughly 12-14 hours/day, just a couple inches above plants(https://www.amazon.com/dp/B005H1C7NA...ing=UTF8&psc=1). I also run a light fan breeze on them for a few hours daily.
• Fertilized at 1/4 strength after true leaves established & also 1.5 weeks later - this may have been a bad idea? Not sure I did that the first year. Used this fertilizer (https://theurbanfarm.com/legrpa.html)
• They seemed to grow well at first but are now somewhat stunted, small & a few are starting to yellow.
• Potted up to 18oz solo cups last night, burying deeply up to tops. Used this soil to pot up since I had a new bag on hand (https://www.foxfarmfertilizer.com/it...ting-soil.html)
• Last night I also moved them out of the house into the garage, which allows enough room for the light with the taller cups. It's a bit cooler in there but outside daytime temps here at in the 60s-low 70s.
• Plant out date should be in 2 - 2.5 weeks - any chance you think they'll be large and strong enough by then? Any tips going forward?

Thank you so much for any help!