Have a 2008 Trek Portland. Having shifting issues in the rear with the my current 105 group set-up. So, I've decided to use some extra cash and buy some 105 5700 pieces. So far, I have the chain, rear derailleur and cassette. Now I am looking at crankset, bottom bracket, and front derailleur.

Questions:

How do I figure what length crank arms I should get?

Should I replace the bottom bracket since I will replace all other drive train parts?

How can I tell if the front derailleur shoul be replaced or should I replace since I'm replacing all other parts?

Thank you in advance for any tips, hints, or suggestions.

J