Growing lettuce will this work?

[Jetstar]

I'm going to grow lettuce in my smaller 4gal. grow bags, saving the 7 gal. bags for my indeterminate tomatoes. I want to start 2 seeds per pot and after 3 or 4 weeks I'll place then in the 4gal. grow bags, 8 plants per grow bag. Here's what I'd like to do since I only have my small grow light set up and its in use. Put them in our S. window or outside weather permitting when possible, I think this should work but i'd like to hear your thoughts or concerns... Thanks