Quite same guide when i use for my first rooting and flashing but different site.
1) Desire is newer, nexus one older, but they are brothers! the closest one i've ever seen...hehe...and nexus one are not produced anymore. well let others tell more about it as I have only use Desire only so far. Never touched N1 but i would love to!
2)If you mean 3g by browsing and such, i never experience those, as i'm online most of the time...and i'm pretty sure Desire dont have the front camera so i know you mean the browsing and such right? huhu...

just make sure dont use it while you're charging, or else it'll be hot like a BBQ...

3)Depends. if you use lots of widgets that sync at specific time intervals on your homscreen, then might not. Not sure bout this, i have mine at 12 hours at most using a custom rom that is. with the stock rom, only 6-8 hours. some can get to 2-3 days but usually they turn off their wifi/data while not in use so thats why.
At the very first use you'll notice the battery will drain fast as hell. but in a week, it gets better. and there's a method to bump charge your battery too! i found my battery up to 10 hours so far with heavy use; 4 - 6 hours on wifi/data, normal msg/call usage (sometimes chatting with girlfriend, you know how long can it be..

), youtube, camera/video recording(720p), and downloading stuffs from market too!...10 hours is quite good la for me.
Well, most of the guides are same with just some minor tweaks here and there. I got confused last time due to certain small differences but again, all of them achieve the same objective
Bump charge never exactly worked for me. Even if it does, its barely noticeable on my side. I am still getting about 1 1/2 day of usage, with occasional browsing, phone calls, SMS, music listening and games.