Few advises needed

[javafxnoob]

Good morning, fellow tomatovillians

I can't wait to start my seeds for my second noob season. I was overwhelmed with my cherry tomatoes last year, hope to get even better results in 2017.

Plan is to correct some errors from last season like too close planting, garden protection from creature with sinister name "rabbit", to improve watering... And of course to plant my tomatoes earlier than last year for sure.

Today I am going to look for some material for my cold frame.

I would need few advises however. I would try few approaches in seed germination, still experimenting. Plan is to try 2 seed per container cell and to try dense planting in container cells like on Craig video's. I liked that indeed.
Maybe will try few small pots in my room windowsill to see how that will go.

What would I like to know when seedlings grow enough to be transplanted in pots, what size of pots do you use for single seedling? I don't want to transplant them in bigger pot after this initial transplant, they will go straight to garden.

Serbia is in Europe 7b zone, so my plan is to transplant in garden in the second half of April.
I have few indeterminate hybrid varieties in mind, maybe few plants of cherry, but thinking to try some nice heirloom varieties so I can at end of season preserve seeds.

Do you have any advises what variety should be doing well in my zone? Possibly some that would be easy to grow for beginner gardener and not hard to obtain. Red color for now, not yellow or black.
Not sure where to buy heirloom seeds, in shop where I buy materials only hybrids.

Thanks in advance, God bless