Well of you've got an experienced mechanic with you that will definitely help. The install isn't hard, just time consuming really. To find out what fear ratio you have you can look at the RPO codes in the glove box. Here's a list of the gear codes and what they mean
GQ1 -- AXLE REAR, STD RATIO
GT4 -- AXLE REAR, 3.73 RATIO
GT5 -- AXLE REAR, 4.10 RATIO
GU4 -- AXLE REAR, 3.08 RATIO
GU5 -- AXLE REAR, 3.23 RATIO
GU6 -- AXLE REAR, 3.42 RATIO
G80 -- AXLE REAR, LIMITED SLIP (POSITRACTION)
HC4 -- AXLE REAR, 4.56 RATIO
If you have 4.10 or 3.73 then you'll be a little under geared for 35's and you won't have as much power but if you have 3.42's, I'd look into regearing.
And if you're lifting soon, just wait on the alignment because you'll need one afterwards