A typical pulley install should take ~30 minutes. If you run into problems, it can be a lot longer, but the only real problems you can run into is the tool breaking. I have had this happen to me on two occasions and it set me back a few hours each time. (one time was actually a little more than a few hours) Anyways, I would have someone install it for you that has done it before, and try to use someones tool who already has one, instead of renting or buying one. As for mods, from my experiences, you really should have a lot of stuff before you put on a 3.4 pulley, but most people don't want to invest that much money, so I would recommend a t-stat and colder plugs, which you already said you were gonna buy so you will be pretty much good to go...however a CAI would not be a bad idea. The computer should take care of any knock problems you have, although I think I would try to open up the exhaust and intake a little more to be safe eventually.
1990 Maroon Grand Prix STE McLaren 3.1 Intercooled Turbo, 14.695 @ 94.49 on 12psi before cam/heads/etc.
1990 Bright Red Grand Prix McLaren 3.1 Intercooled Turbo, 14.819 @ 92.72, 189whp
1999 Grand Prix GT 9.75:1|K&N|160 tstat|No Ubend/Cat/Res|UD Pulleys|Ported M90/TB/Heads|XPZ|2.55"|Pacesetters|Stage 2 I/C. 12.442 @ 112.78
2000 Blue Bonneville SSEi Supercharged Gutted Airbox|K&N|3.4"|1.9'*|WP Pulley|Custom DHP|180*stat|41932'*|No Cat. 14.681 @ 94.80
2002 Dark Cherry Grand Prix GTP Supercharged & Intercooled
12.084 @ 114.38 w/1.743 60', 315.6whp, Fastest Stock Cam M90 GTP!
NOW XP CAMMED, 340.6whp with XP, stock heads, Gen 3 M90, 11.984 @ 115.84 w/1.750 60'!
Most HP Stock Heads Gen 3 M90 GTP!
2004 Red Monte SS Supercharged K&N|3.4 Pulley|1.9'*|180*stat|41919 plugs|3" dp|No cat/ubend|DHP|Shift Kit. 14.2 @ 98
GOT BOOST??? Friends dont let friends drive stock!