Well it is still way too early for me here so I'd bet it is way too early for you. ;)

I don't recall off hand the plant out dates for Zones 4b and 5a (mine is April 20). I think it is about May 15th for those zones but you can easily find out what they are for sure. Wait until 8 weeks before those plant out dates.

My plan is to start the seeds in paper towels and baggies, then transfer them to small pots. I will be using only natural light, and covering them with clear, ventilated plastic.

If you want to germinate them that way that's fine but the vented plastic is only needed for the germination phase. kKeep them covered after germination and you can almost guarantee damp off. So you won't need it. Natural light is far from ideal - it creates limp leggy plants. Plenty of discussions about that. Please consider supplemental lighting.

You'll likely discover that an interim transplanting is also needed. Go from germination in the bag to a small container like an 8 oz. cup and then to a larger container - many use 16 oz. plastic cups for the final stage.

Good luck. :)

Dave

PS: don't forget to check out all the FAQs and Growing from Seed info available here and on the Growing from Seed forum too.

Here is a link that might be useful: Growing Tomatoes from seed FAQ

Good post Dave. I started 200 seed inside for the first time, become lazy for a few days, and watered too much, and ended up with 70 or so good-looking transplants.(under 34-watt shop lights)

All in cups, deciding they were not getting enough light, moved them outside on the porch. That was 12 days ago and have not watered since.

I am a newcomer as well, and what I learned is to not overwater when it comes to the seed.

Now, they are doing really well.
Now, they are looking really well.

My porch is different than your porch right now though. Down in Southeast Texas, we have been sitting in the mid 60's for about a week and a half.

I agree with Dave - It's still too early. I'm in zone 6 (southern CT) and I usually start mine the first week in April. Your paper towel method seems very labor intensive. Why not get a plastic 72 cell starter tray. They're not too expensive. Pro Mix works for me too.
John A

The nice parts about the paper towel method are that
a) you get really good moisture contact for germination and nothing dries out
b) you only plant the 'winners' which are showing germination
c) since you only plant the winners you have a space efficient planting plan
d) you may waste fewer seeds since you'll only put 1 in each pot as it germinates and not have to cull within a seedling tray

The bad parts are that
a) it is much more labor intensive
b) you waste almost as many seeds (if you are like me)

By the way, I would use unbleached coffee filters and zip lock bags. It can be difficult and lethal (for the seeds) to try to separate them from the paper towels due to the size of the weave; the root tends to wrap itself around the fibers and it can't/doesn't seem to do that with the coffee filters.

I've done it with coffee filters and trays; I'm using 72 cell trays this year and trying to limit the labor intensive parts of seed starting (while still growing exactly the stuff I want v the stuff the big boxes will sell me in 10 weeks). I do have the space, so that's a lot easier.

When I was doing the coffee filters I would just drop the bags on top of the heat register on the downstairs bathroom floor - I did get some of the fastest germination I've ever seen. In the end though, all the growing tends to even out.

Andrew