Hello Tek, And i observe the Saturday Sabbath (i live in wales so thats GMT), so sadly wont be available on 19th, however i can advise you before or we could attempt a transfer in weekday or sunday.
Unfortunately, Saturday, Sept. 19 will be the only day I have available to migrate the forums as I work Monday through Friday, my wife works Tuesday through Saturday, I've already cleared it with my wife's parents to watch the kids on the 19th (I'm usually solo with my 2 young daughters on Saturdays), and I don't dare try to schedule anything that requires focus and a dedicated block of time on a Sunday as that's the only day all of us (me, my wife, and my 2 daughters) are together for the whole day.
I may be able to set up a dummy site ahead of time and run tests before Sept. 19, though. If I get the opportunity and get a test site built, I can send you the address and any questions I might have, if that's okay with you.
Things to consider
Set up a test site first and do a dummy transfer to ensure all data moves smoothly.
Agreed. I...just don't know when I'll have the time to do that before Sept. 19.

If I can do one step now and another step later and yet another step later, then maybe I can make something work (and with a test site not in public view, I think that should be feasible).
Then start a test site which will have all addons, skins etc ready but no content, this will be the base for the live transfer, all the data will be imported into this one.
A good plan.
As for Web site theme/skin do you have one picked already? if not i could work with you on creating one (free of charge)
A custom theme or skin right out of the gate would be fantastic and above and beyond what I'd hoped for. I'd tentatively planned to run the stock theme until I or someone else had time to choose and install a new theme.
But if you're willing to work up a custom theme, oh my word, that would be fantastic. Even changing the palette on the stock skin--something to set us apart from the default, which is something we've never done with vB4 in the years we've been using it--would be most excellent.
I'm a big fan of high contrast/"mild" colors (my vocabulary escapes me; I'm thinking of colors that don't smack your eyeballs with a 2x4--no red text on black backgrounds, for example), but I'll defer to others for requests on specific colors. As long as everything is functional and I don't burn the forums down, I'll be thrilled.
As for server, what type of power do you have vps, shared, dedicated etc? will determine the speed.
Dedicated. If you'd like, I can contact our server hosting provider and ask for the specs of our server.