You need to say which flowering plants you intend to grow before people can advise you. And are you asking about pots just for seed starting? Or do you wish to grow the plants in containers all their lives?

seeds are usually started in flats .. and moved up thru a range or pot sizes ... until it is time for them to go into mother earth ...

https://duckduckgo.com/?t=ffnt&q=seed+flats&iax=images&ia=images

and thats the part you dont mention... are you growing in pots all season ... or do you plan to plant them???

next.. the most important thing in a flat or pot.. is the media ...not the plants... its a water management system ... it either makes things very easy.. or harder than it need be ...

and then timing is very important ... if you plan on putting them outside ... and we would need to know where you are .. big city name.. to help with that ...

and then of course.. all the other variables .... including supplemental light if you are starting indoors ...

ken

+1 Ken. Everything I grow--with a few exceptions!--starts in flats of 72 cells. Most stay there until they move outside in May (in Pennsylvania) and are grown under fluorescent light in the cellar. 12 flats a year, about 865 plants (there are always a few extras hanging on the fronts of the rack).

The exceptions are the things that don't transplant well. Morning glories don't transplant well at all and I tend to plant those where I want them for the touchiest varieties, or in larger pots and hope for the best. Even so, about half don't make the transfer.

I'll be happy to detail out my system if you have any specific questions. It wasn't even all that expensive.

Personally, I just use Miracle Gro Moisture Control soil. Works like a charm. And a 2 gallon watering can to cart water down from the kitchen. It's not really much effort, just be careful not to overwater. Feed very lightly while growing indoors. Never had a major problem.

My cycle's about to start again for this year in a week or so with the Profusion zinnia, which need a lot of development time, and the decorative eggplant.