Looks like you are off to a good start on a terribly fun and addicting part of gardening.
I think anything that will hold soil and lets light in can be used for seed starting and recycling what you have for containers is great.
You said you are limited by shelf space under lights , If you have an outdoor space you should check out winter sowing it is great for many plants and a lot less care is needed. You may be able to expand your variety greatly with not much effort.
