Well, i'll try and answer as many questions as possible.
To start a team, you decide to start a team, signup, pay, and bam, ur an FTC team.
Right now FTC is going through a platform change. This year we built on the VEX robotics system but next year, we will be building on another kit, slightly better and more expensive.
There isn't a minimum, but there a 10 people maximum.
You would register at usfirst.org and then you have to separately register for your regional/event. You local regional can be found at this link:
http://www.usfirst.org/whatsgoingon.aspx . Note: you may have to travel. Teams come from all over and sometimes teams go to multiple regionals. You may also want to think about attending the Georgia Regional.
OK, so the first fee is roughly $300. Signing up for the regional is roughly $100. The new kits next year will be roughly $1000. Then teams always need to order spare parts and extra add-ons to the kits to make them better. So, assume you spend at least $500 on additional parts. So you're looking at roughly $2000, give or take. Fund raising is a huge part of FIRST. This can include local sponsors and some teams do fundraising activities.
Hope this helped. FTC is truly great. It allows for kids/teens to build a great robot, without having the hassle of the huge FRC robot, and without the financial responsibilties of FRC. FTC has amazing games that challenge teams' thought power.
NOTE: Most teams have team shirts. Which will also cost you.