what kind of season do you have? it seems that ours is too short for most volunteers to do much.
if i were going to grow a lot of different OP and heirloom varieties i think that would be more interesting and have a better chance of getting decent results, but i've been banned from trying other varieties now. we have too many tomatoes in storage ATM so it is likely we're skipping a major planting of tomatoes this year and will just put in a few cherry tomato plants.
as for diseases, our location seems to favor certain types of late season blight, but if we can get a crop through the mid-summer it doesn't matter what the blight does. it doesn't ruin the fruit. last season was unusual for us in that the disease took 90% of the crop just in the last few weeks of ripening. greenhouse people said it was last seen in this area 80 years ago. likely weather and growing medium related, but hard to prove without a lab to do the work and ways to trace things...