No, you can ride unattached.

Just keep searching out harder and harder group rides. If you want to race, IMO, you should eventually search out the rides that the racers do. If you plan on only doing crits, search for the shorter, higher intensity rides. When you get to the point where one group ride becomes "easy", try and move to the next level up. Don't be intimidated.

Who cares what your bike is right now. I have 2000 aluminum caad3 triple with mostly 105 parts and I won several races on it and it was good enough to get me all the way to cat 3 (and is good enough for cat 3, regardless).

Initially you will spend more time riding. As you become familiar with the sport/training, you will find out that you can spend less time on the bike and get better workouts. You will become familiar with intervals (beautiful, nauseating pain), rest days, going slower to go faster, etc.

I spend about 8-12 hours a week on the bike (my wife keeps track of it ). As for how much money? Entry fee is about $30 or so a race, so you do the math. Add gas, food, and lodging if you go too far away.

The most important thing is to have fun. If you race race race and don't have fun, you will probably only do it for a year or so. Also a great way to meet people. Try to get to know some of the racers out there. They will give you tips.

And have fun.