Since the others already got here, I'll just give a factual answer to your questions in order

Although it is about a Matisian joining the Kamist cause, you might also find
this thread useful
How tough is it for a Fyros to join the Karawan? // Will that take longer than raising a new Character? Because Fyros start with negative karavan fame, it will of course take longer to become karavan aligned (at +30 fame) but there is no reason not to do it if that's what you want, and there are plenty of people who will be more than happy to help you do it as fast as you like
Do Karawanserai Guilds usually accept Fyros? Of course; very few guilds descriminate on grounds of race - due to the way guild alignments work, each guild can either be Kami, Neutral, or Karavan aligned as well as a racial alignment (see the other thread I linked to above for explanations on what this means) and will usually only pick their guildies based on those factors. Usually Karavan guilds (thought I don't know enough about enough of the tryker ones to comment) will happily accept anyone as long as they fit in with the guild and follow the Karavan way.
Will I get problems on Fyros territory or maybe even elsewhere joining the Karawan? The effect of becoming karavan will affect which TPs you can buy... Fyros lands are unique in that all of their towns are in different zones, which means there is a Karavan TP next to them all (whether or not you'll be able to use these after spires come out is another matter that I won't complicate things with). In other lands you may have to walk further from a TP to get to where you want to be, or yuo may not have to walk as far, but the only places you
cannot go as a karavan are the two Kami temples - one near Pyr and one near Zora. both of these are in such a location that it won't impede your day-to-day life.
Edit: one more thing: how many % join the Karawan?
I hope not the majoriy
Well you can see what an issue this is for some people... personally what other people choose isn't what makes my decision - I know some people like to play the underdog, but I choose the side that is right for me, not the one people tell me to choose

Good luck in your choice and I hope its the right one for you
