Upgrade Hacked v2 > v3 Board

[Intex]

I currently have a pretty old version of vB (2.2.5). As version 3 has been out for some time and has quite a lot of the hacks I used on 2.2.x, I think now is an appropriate time to upgrade.

What I'm not sure about is the method of approach, particularly as I have many hacks already installed (around 50). If I upgrade from 2.2.5 (after upgrading to 2.2.9 I've heard), I assume that next to none of the existing hacks will work any more. This is exactly as I would expect with the new code adopted by v3. However do I just run the upgrade process and then re-install the new hacks for v3? What about all the older code in files / templates? Of course I'm assuming that the majority of the files are replaced but what about the templates / styles etc? Even if this all goes smoothly, does this just leave a lot of other redundant code from previous hacks lying around?

My other thought, was is it possible just to install a fresh copy of vB3, install all the new hacks specifically coded for that version and then import all my users / posts etc. I've not seen anything that will aid in this process.

I certainly won't be the first person to have gone through this process, so any feedback about how you've gone about your upgrade would be most appreciated.

Thanks in advance.