>>111033>and I'm not sure what size container would work bestIt depends on how big you'll let the plant get, and the nutrients present in the soil at the moment. A bigger pot with more soil will give you a bigger 'buffer' with nutrients (or when fertilizing) and moisture. I myself have grown tomato plants a bit bigger than yours in similarly sized pots without running into any troubles.
>I added some plant food todayNote that it will not 'heal' the yellow leaves that already have been drained, it will simply stop the problem from progressing.
Quick release artificial fertilizer will work the fastest, but is also the easiest way to accidentely 'overdose' your plants; causing a sudden large increase in soil salinity will disrupt the roots' homeostasis, colloquially referred to as nutrient burn. Slow release or natural fertilizers will work gradually but won't 'cause any nuteburn unless you go 'full retard'.
>I'll keep an eye on them, but just not try to bother them too much.Indeed, I share your approach. See what works for you. Tomatoes don't tend to be all that fussy. Most people mess up by pampering them too much; overfeeding or overwatering are in my (again humble) opinion/experience the most common mistakes. I hope it all works out for you. Let us know
Pic unrelated; my gf's bunny kept me company while gardening today :3.