won't be laggy but not advisable if you're running heavy softwares

8GB RAM if you're using Bootcamp is plenty enough. Virtualization via VMWare/Parallels? Well, we've been through that debate/mess/arguments a few pages before, and I don't want to go there again.

basic work only should be ok for VM with windows installed, i have tried (just test) play diablo3 inside with everything set to the lowest so far still acceptable. anyway, for microsoft words those there is mac version.
Better use bootcamp if wana use windows to play mid and heavy game / application.

not reli, depend on what you need the windows do
from what i know the most stable booting in windows has 3 option:

1. Bootcamp
Pros : your macbook can completely 100% become a window pc
cons : must restart and choose to boot into windows, also means u cant use OS X in the same time until u reboot again.
          Have to isolate your hdd in to windows and Mac. example: total 250gb drive, u have to choose how much for OSX and    how much for Windows, then both of them cant share the space after decided.

2. VMware fusion
Pros : can use Windows and Mac togather without restarting, can share file at OS X desktop and other drive, use around 10gb space for windows only, good for testing stuff / light software only.
Cons: will have slightly lag when loading stuff inside vm, eats lots of RAM (atleast 3.5gb), can run heavy application but will laggy, not every software from windows support vm (i heard from my colleague which use OSX too, i nvr encounter that yet)

3. Parellel desktop
Pros : somthing like vmware fusion, but this application can run at background of ur OSX, means when u double click .exe those at OS X, it will straight promt out the window base installer etc to let u directly run those thing at OS X.
Cons : I feel abit more laggy when opening and runing software in parellel then vmware fusion, so others i not reli sure..

anyway, above those is my personal experience, doesnt mean all is correct but that is my personal opinion only hehe. u may try ask other and see >.<

Glad that can be help share with us once you get ur mbp sure no regret getting it