Well it can take disc brakes, so you are good there. If you are going to be running the same size rotors you need no adapter. If you are going to be running a larger rotor in the front you would need to appropriate adapter for the size. Make sure you get the mountain version of everything. BB7 also come in a road version which would not work.
Replacing the crankset often comes with replacing the BB too. You can also replace the chain rings individually. If the chain rings need replacing, the cassette and chain more than likely needs replacing as well.
I run SLX front/XT back and Deore shifters with good success. I had a deore front, but it broke pretty quickly. The SLX seems way more robust. If you keep with a 9 speed cassette you will have to run a 9 speed rear der. If you keep everything Shimano you shouldn't have any problems.
The diameter of the handlebars are important. It doesn't show on your link what size they are. Common diameters are 25.4 and 31.8. If you don't have one of these I would upgrade your stem to one which accepts 31.8, which is the more common of the 2.