Meso and Thermo are broad generalisations, or categories, which basically refer to the idea that some cultures work best at lower temperatures (usually best under 35 C) and some work best at higher temperatures (over 35 C). So "meso" and "thermo" really refer to the temperature range that a culture is suited to (think rule of thumb here, rather than carved in stone though).
Now, what those cultures do with respect to flavour, depends upon which one you use, and which strain you use. For example, "flora danica", which is a meso culture made up of 4 cultures, has the same 4 cultures as cultured buttermilk. However, the strains will differ, and the proportions will differ, so you won't get exactly the same result using buttermilk as flora danica. Other "meso" cultures will have 2, or 3, different types of cultures, and you can buy singles as well (which allows you to vary the proportions of each type/strain yourself).
If you search around on the forum, you will find various discussions on what each of the cultures do and what they contribute to the flavour development. Aroma B is similar to flora danica, and both produce buttery flavours, etc. Buttermilk works fine as well. You will get some differences in outcome if you use a different culture mix, but in my opinion, when you're starting out, just use what you have. Learn to produce a decent cheese, that ages well, doesn't crack, and tastes good. Once you've got your techniques down, then start fiddling around with different culture mixes and see how things change. Build a skill set by keeping some things constant, then have some fun by changing something.