Just a reminder of what you should be starting indoors. Virtually all transplants that you wish to plant out come mid to late May should be started now: peppers, leeks, snapdragons, alyssum, tomatoes, zinnias, asters etc. For a more complete list, check out my blog post A Seedy Pastime.
AND don't forget to use Mark's Choice worm castings & Pro Mix when sowing seeds. Mix one-part worm castings with 10-parts Pro Mix for very best results.