Alright, thank you for the kind replies everyone.

I've figured it out (mostly) to make this work without leaving a trail of fire behind on my finance. :)
I'll start out with 2 new battlechests (40€ in total, WoW + BC) it'll take a while to level up them all 70 anyway + I'm still planning to raid on my actual main.
This month's salary has gone mostly on new furnitures (new apt :3). In next month, I'll use part of my salary to obtain WotLK+Cata x2.

I'm obviously going to level my toons with RAF, however I've got one more question regarding the matter.
If I order battlechests today (likely will arrive next week) do I have to create accounts now, use my 10-day trial or can I open accounts next week, RAF both and upgrade them up-to BC?

I checked the RAF site over @ Battle.net, and I got the impression I can open accounts and upgrade immediately without a hassle.

Also, thanks for the nifty advice Littleburst!