I would talk to FRC team 4481 Team Rembrants who also is based on the European Continent (I believe in the Netherlands). They will probably be best able to help you with European specific challenges (travel, ordering parts, etc.).
As far as in general, you will likely need money to register the team, buy parts for the robot, help with travel costs and much more. Team budgets vary, with the lower end running off of about $10000 - $15000 American, and an average team probably spending ~$25000 per year. I'm guessing because of being in Europe, you'll need to strive for a bit more than the lower end to be able to compete at all, so finding sources of revenue for the team through sponsoring companies, support of the schools in the area or diligent fundraising will be important.
Second, is mentors. Almost all sustainable teams have at least a handful of technical and non-technical mentors. While every team structures the interaction between mentors and students differently, most teams will agree that having the guidance and leadership of mentors is invaluable. You can maybe reach out to technical companies to see if any of them have volunteer programs and could send mentors over. Our team has personally recruited mentors from the parents of our students. I'm sure others have plenty of ideas for this.
Third, and most important, is students. Do you have a school or community group from which you can get students? How do you plan on advertising to them and ensuring that people actually show up?
BTW,
this is the contact page on the rembrants website. I don't want to speak for them, but, if I remember correctly, they are the ones that want to get an FRC regional in Europe soon, so they would likely be willing to help you out.