You won't have to purchase the stock tune, DP will put it on there no charge.
As long as your motor is healthy don't worry about the mods. If you think you have problems with injectors, HPOP, whatever I'd take care of those before adding the chip.
For gauges Autometer, Isspro, and Dipricol are the popular choices... none are too cheap. Stay away from the cheapy Glowshifts on Ebay... I've heard a lot of bad things about them.