I've got my spearmint in a pot which measures about 80cm, and it needs to be regularly repotted. All I do is remove about half the plant at a time, discard it (or give away), and replant the other half, using fresh potting mix to fill in the gap. No matter what size pot you choose, you'll have to do this. Clearly, the larger the pot, the less often you'll have to do it - but make the pots a manageable size to work with!

Yes, mint propagates itself and spreads by runners, both over and under the ground. These runners form roots - hence a continual supply of new plants! Spearmint and its relatives produce seeds, and self-seed readily. Peppermint and its relatives don't. Lemon Balm does.

There are around 600 species of mint, so it's a matter of trial and error - just keep your mints in separate pots!

Check the many mint questions posted recently.

Mint will quickly take over via runners. I always plant in at least a 12" pot to begin with. A larger pot would be fine too. Mint likes to be moist so a large pot will help prevent the roots from drying out, especially where you are.

Spearmint, Mentha spicata produces viable seeds.
There are at least two types of Applemint:
M. xvillosa is a hybrid that may not produce viable seed.
M. suaveolens may produce viable seed, but I haven't ever had a seedling.
There is another, less common, "applemint" out there -variegated applemint aka ginger mint, M. arvensis, that is seed fertile.

If you cut back the flowers you won't have to worry about seeds.

Scents/flavors of mint will NOT intermingle when grown together. This is a popular myth, but it is just that, a myth. While the myth plays to our sense of herbs having "magical" properties, it simply doesn't happen.
Many mints (Mentha spp.) are very fertile and hybridize readily with each other-especially spearmint, M. spicata, and watermint, M. aquatica . These hybrids can vary wildly and can be one-of-a-kind, never to be duplicated. Even true M. spicata seeds produce offspring that vary from and are often inferior to the parent. You'd be amazed at the variation in M. spicata alone. I have some with narrow, gray, wooly leaves and some with curly green leaves. Sometimes, though not usually, the runners may produce a variable, less culinarily desirable, plant as well. This variability has been misunderstood and undoubtedly led to the myth of "Magical Change".

F. DeBaggio

Mint works great in pots!

Yep, it works great in containers. I have Mint, Chocolate Mint & Lemon Balm all growing fine & beautiful in some 3 gallon pots. =)

I have a follow up question. Should I cut back the flowers? I like the idea of having mint seeds to plant but I don't want to reduce my yield (as measured in mojitos) Thoughts?

You many not like the plants that you grow from seed. Some mints, like peppermint, produce seed that is not viable. Cutting back most plants in general will increase overall yields. Once the mint flowers, it focuses its energy there which slows down leaf production.

F. DeBaggio