ok... let's see:
1.your choice for processor, ram > 3 gb.. depends , bandwidth.. i saw somewhere that you can have 1k players with 30 mb.. but more is better (more mb ofc)
2.linux vs windows.. for hosting a server i would say linux
3.i'd suggest to host it yourself.. dunno if dedicated servers will approve wow servers or so... and it's more easy to handle if it's near you
tips:-for actual playing you need a lot of hacks.. or so called cuz... players want functionality and so on... that mangos doesn't has .. yet (my opinion)
-advertising
-do it blizzlike.. not a funserver-it's not fun at all
hope it helps
pm me if you need more info