It's your map so you can do what you want. The thing to be concerned with is that the shape of the world is the basis upon which any other degree of realism are based. Climate, history, navigation, etc. all depend on where things are, and the basic shape of the world. So if the shape is a sort of inconsistent kludge, so will everything else be, regardless of how much thought and effort you put in. And the more work you put in, the more it will hurt if you hit a point where you really need it to make sense on a globe because at that point you'll have to go back and rework everything from the ground up.
Originally Posted by SkullCollector
That said, plenty of fantasy worlds don't make sense as spheres. Many combine a restricted extent and a low level of cartographic sophistication which allows them to treat the portion of the world they know about as being flat without getting any more distortion than their surveying would introduce anyway. Others are outright flat or cylindrical. Some even have strange properties like a euclidean distance metric but a toroidal topology.
In the first case, a continent is a HUGE place for people who don't have any transportation technology more advanced than a horse and cart or a trireme. You should also remember that it's much harder to move north-south than east-west. That's though to be one of the reasons that Eurasia had a much better trade network than Africa or the Americas and why Europeans had contact with China long before reaching sub-Saharan Africa. Sticking to just a temperate continent would still give you plenty of space for a fantasy "world" while being much easier to map than a full globe.
You could also make your world flat. In this case "north" and "south", or "latitude" and "longitude" as we know them become meaningless, although you could use the worlds to refer to some other set of directions. A flat world is a world where you need a lot of magic to make it work. That gives you a lot of flexibility, but you do need to be aware of it, and you should try to avoid introducing any 'spherical' concepts accidentally without accounting for them. For instance, being able to figure out where you are by looking at the stars, the climate varying with latitude, and the seasons are all based on a spherical world. A flat world would be different. Navigation might be based on a network of magical beacons or ley lines, and regional climate might be influenced by the personalities of the gods who reside in particular areas and seasons might be due to the sun god going on a bender once a year and being hung over for several months.
You can always change how the planet itself acts in the universe to make the map fit. I wouldn't delve too deeply into your climatic/geologic details. As an earth scientist who makes rpg maps for a dnd group, I get pretty deep about the world's geologic stuff, but the players never realize or look into it. Just keep having fun with it, if you want southern warm climates then just tilt the planet like uranus, or move it closer to the middle of the star system. Unless you are playing the rpg with a bunch of scientists (my world) then leave stuff open for question. Might make for a quest or some interesting lore someday when an adventurer prods deeply. As for political boundaries, I normally just cut up the continents in as many ways as I want and come up with an explanation for each one later. I know you said you were going to put this one off, but I figured you would still want some advice for the map later. Oh, and have fun with it! :)