tomato blight is a fungal infection, so you want to make sure the plant's leaves and stems are able to dry thoroughly after wetting. When watering, do not wet the foliage. Separate the plants so they do not touch. make sure they get full sun. water in the morning so there is ample time for the soil surface and and leaves to dry out. allow the soil to dry down at least an inch from the surface before watering again. This will make sure fungal spores cannot germinate. Try not to splash water on the soil surface onto the leaves when watering.
If you're going to go with containers, which is a great idea, get some big black nursery pots. 15-20 gallons is best. 5 gallon pots is not enough root space and won't hold water for very long. The black pots will warm the soil quite a bit, which tomatos love. Make a soilless mix of peat and perlite(60% by volume or so), a bit of sifted garden soil(say20ish% , and worm castings(about 10-20% worm castings is good). The mix should have very good drainage. Also mix in an organic fertilizer such as a seed meal with an analysis of 5-5-5 or so. Organic fertilizers are naturally slow release and do not cause salt buildup like chemical fertilizers(important in pot culture). Occasional watering with liquid kelp and fish emulsion will make for very healthy plants(say, every 1.5 weeks at recommended dosage)!
Water your plants until they just start to drain, then stop and water down the line. Go back to the 1st plant and put in a bit more water and go down the line. This will make the soil expand and hold a ton more water.
Make sure your fertilizing regimen has a source of calcium and magnesium to avoid blossom end rot and to help resist diseases.
good luck and let us know how it goes!
-fixie