Looking to start a skoolie adventure!

[busbuild]

Hello, and thank you skoolie.net for all the information and inspiration I've already gotten. This has been an incredible community to stalk the last few months while doing research, planning and dreaming. My family is finally at the point to start turning those plans and research into reality, but wanted to reach out for my first bit of advice from those with more experience and knowledge than I have currently.

General bus configuration (engine, transmission and rear end) that serves well in cross county travel, especially in mountains and canyons.

So far I'm sold on a DT466E engine (but could be talked into something else if a compelling argument was put forth), but its the transmission and rear end that I've had a hard time researching and understanding. Everything around me seems to be automatic, which means it's going to be an Allison but of which flavor? I'm in an area with minimal elevation change, and I'm sure buses are spec'd by the school districts for the flatlander needs. My family plans to do plenty of mountain exploration which is causing me to wonder if I need to look for buses in other areas, but that brings it's own complications of not being able to really check a bus out before committing to it etc...

Are there any models that should be avoided (besides the AT545), or models that I should seek out? I mostly see 2000 Series around me, but is it worth the effort to find a 3000 series?

What are your thoughts on this theoretical setup (my current realistic ideal I'm thinking): DT466E, Allison 2000 Series, Rear ratio of 6.17, 30' CE

Am I going to be able to do 65 on flat ground? Make it up hills without smoking a tranny or rear end? Make it down hills without careening off a cliff?

Thank you for any and all insights!

Also, any incredibly well documented roof lifts? I need to show my wife that, yes it is a lot of work, but is totally doable.