You don't need any lift in the rear. Personally I would just do the 2.5" level in the front and leave the rear alone.
What kind of leveling kit are they proposing to put in the front? I'm assuming a spacer? It won't ride like crap, it will be very close to stock. However I would recommend a set of Bilstein Adjustable struts for the front end instead as they are better for the front end components and will provide a nicer ride than stock.
I fit 275/65/20 Rocky Mountain ATS's on mine with no level at all, no rubbing, etc.
Definitely do not need a lift in rear.
If you are going to bring the front up, I (and many others) would recommend Bilstein 5100 Adjustable shocks. They are 100 times better than any type of spacer lift and ride much nicer than the stock shocks.
I had a 2 inch front spacer on my truck for a little over a year, caused me a few small issues - had to replace factory shocks twice, uneven wear on front right tire - may or may not have been directly related but that's my personal experience.