There are different types of grow bags. The regular kind, and the upside down kind.

http://www.cleanairgardening.com/tomato-smart-pot-planter.html

http://www.cleanairgardening.com/totuupdotofl.html

With a regular grow bag, you can start from seed or a starter plant. With a Topsy Turvy, you’ll have to start with a starter plant.

The most important thing, in my opinion, is starting out with a high quality potting soil. The better the soil quality, the better you’ll do.

Here’s a good article about potting soil.
http://findarticles.com/p/articles/mi_m1082/is_3_43/ai_54851905/

I love the Square Foot Gardening soil recipe, which also works well in containers.
http://www.mysquarefootgarden.net/mels-mix/

Good luck!

Good question. It appears that it is possible that seeds can be infected with early blight.

Here are a few good resources for you.

http://www.umassvegetable.org/LateBlightAlertforTomatoandPotato.html

This Cornell link has a list of 8 good steps you should take.
http://www.nysaes.cornell.edu/pp/resourceguide/cmp/solanaceous.php#d5

1. Use crop rotations of at least 3 years to non-hosts (away from tomato, potato and eggplant).
2. Provide optimum growing conditions and fertility. Stressed plants (including drought) are more susceptible to early blight.
3. Stake or cage plants to keep fruit and foliage away from soil.
4. Drip irrigation is preferred, or overhead irrigation starting before dawn, so that the plants are dry early in the day. The key is to keep the period of leaf wetness to a minimum.
5. Mulching helps to prevent splashing of spores from soil up to lower leaves.
6. Indeterminate tomato and late-maturing potato varieties are usually more resistant/tolerant to early blight.
7. Early blight can be seed-borne, so buy from a reliable supplier. Hot water seed treatment at 122°F for 25 minutes is recommended to control early blight on tomato seed. See chlorine treatment procedures under bacterial diseases.
8. Disinfect stakes or cages with an approved product each season before using. Sodium hypochlorite at 0.5% (12x dilution of household bleach) is effective, and must be followed by rinsing, and proper disposal of solution. Hydrogen peroxide is also permitted.

If the blossoms are NOT turning into tomatoes, here are some potential causes:

# Temperature Too High or Too Low
# Lack of Pollination
# Nitrogen – Too Much or Too Little
# Humidity Too High or Low Humidity.
# Lack of water
# Stress from insect damage or disease

http://gardening.about.com/od/problemspest1/a/BlossomDrop.htm

The blossoms are what turn into tomatoes. So it looks like you’re doing well!

Here’s a good Oregon State University Extension page about the subject.

http://plant-disease.ippc.orst.edu/disease.cfm?RecordID=1077

Cold weather during the fruiting period is one cause of cat facing, and herbicide use near the tomato plant is another one. Anything with 2,4-D can hurt tomatoes. Lawn type weed killers near your garden can be a culprit, if you use those.

Here are some varieties that are resistant:
http://vric.ucdavis.edu/veg_info/catface.htm