Unless you are very familiar with parts available and lots of technical details, it would be good to work with a shop to make sure that all the parts you buy will work together and will work with your frame. You need to know what length derailleur cage to get for your chainring/cog combinations. You need to make sure the chainline will be correct. You need the correct reach on the brake calipers. If you order through them and they find a problem, they should correct it, but if you've bought the parts you'll have to buy something else.