Interesting one. Hard (without cheating), but quite possible. I already did it. First of all: declare war on a small but distant, high civ nation (Crete?). After a year or so without any fighting it should be possible to sue peace. Make sure you give them a minimal monthly tribute. This will make your own civ rise quickly, enabling you to colonize quite soon.
In the meantime: Get a 9 + general and an mixed army of HI and archers. It should be as big as you can afford. Maybe max 3 of each, total 6 units. no mercs though, too expensive! immediately (even with a 4 unit army) go into the barbarian provinces bordering you, and provoke them to rise. First the smallest ones, then with raising experience of your army, bigger ones. Constantly fighting those barbarians will make sure, that they will never grow big enough to be a real danger. Finally do the same to the barbarian provinces north and east of you, even the far ones, because they will most likely come for you as well some time. None of these provinces should grow bigger than a population of 4 barbarians
and thats it! with this strategy you have a fair chance to reach 50 % of civ in a couple of years / decades. then immediately chancel the tribute and colonize. make sure you get grain to your capital very quickly, because you will need the population. from there on it is just about expanding, maybe even conquering some gaul tribes (preferably the British ones - make sure you don't border Rome) and so on. until, of course, you inevitably boarder the huge Roman empire, which smashes all you build up in no time and ends the game

you might try and get allied to them though, or at least to give them military access. this will win you some time.
after this you will have to compete against the big players and try to take away their land. But this is a completely different game again. Anyway: playing a tribe like Suebi can be hugely entertaining, confronting you with always new and growing challenges
good luck!
ah, and don't chose republic, but monarchy, when the choice pops up