The lettuce will do well with afternoon shade. Tomatoes and peppers need at least 6 to 8 hours direct sun to produce fruit. Tomatoes and peppers also require large containers, and if you're growing indeterminate tomatoes these will get quite tall and will need to be staked. If you have sufficient sunlight, determinate or patio tomato varieties would be a better choice for a porch.
In the South lettuce is an early spring/ late fall crop. It may be too late to plant lettuce for a spring crop. Lettuce bolts ( sets seed ) in hot weather which turns it bitter. I don't know what your zone is, but I'm in zone 7b, and I planted my lettuce March 5th. I'm harvesting now, and it should last until about mid May. There are bolt resistant varieties, check the packages for this. Lettuce is easy to grow from seed.
