I personally haven't dealt with any companies, BUT consider this- when I went on my tour of Italy for 6 and a half weeks, I was totally unprepared, took everything but the kitchen sink, did 0 training, and didn't even break in my new bike before I left. HOWEVER, I had a great time and no problems. I am going to do it again, but this next time, I will have a better idea of what I should do.
Do you need a tour company? Probably not. Between you and your friends, I'm sure you guys could figure out what you needed to bring. I would suggest picking a country and doing plenty of research on it before you leave. Get a guidebook like Lonely Planet or Rick Steves or Rough Guides to take with you. If you have any questions about touring in the meantime, feel free to post them here where people can answer your questions. You and your friends may want to consider taking a day trip on your bikes someplace close to home with an overnight stay (camping someplace, so bring a tent or stay at the local youth hostel). Since you're not leaving until late summer, you should have plenty of time to get ready for this- you can take several day trips and build up your confidence. When taking your day trips, take all the equipment you planned on bringing so you can get used to carrying larger loads.
I think tour companies are ok, but I do think you lose some of the freedom of making decisions that work for you. I personally would not work with a tour operator- I like making all the decisions for myself and not being given a timetable or told where I should go or shouldn't go. Some people like having everything done for them, I do not.
Where are you thinking of going this summer?