RB750GL Home network individual users bandwidth control

First off sorry if this is a repeat question (the more i read the more confused i get).

This is all for a home network. I have capped internet(60GiB/month) that goes from the modem into a wifi router(crappy dlink without dd-wrt support). all clients are wireless with the exception of a blue-ray player(can be wireless if it simplifies things). I have a RB750GL that I would like to put between the modem and Dlink. now what i’m trying to accomplish is to have the entire network traffic monitored and disabled when we reach our cap (10$/GiB overage charges). I would also like the mikrotik to identify and monitor guest internet usage (and possibly some logging if its simple) then at some specified traffic amount eg. 1GiB to slow their bandwidth to something around dial up speeds then when 2GiB is reached cut them off entirely. An important requirement is that LAN traffic be unaffected by this limiting/disabling. At the end of the month I would like the usage stats to be reset back to a 1GiB and 2GiB limit respectively

scenario:
My friend comes over to play some minecraft, while we play he has some updates and a movie downloading. once he reaches the 1GiB mark his downloads should slow down but our LAN gaming should be unaffected. then when he finally reaches the 2GiB limit he should be unable to do anything on the internet(web, email, downloads) but should have full speed and access to the LAN environment so we can continue to play minecraft.

I think that this requires a queue but i’m an absolute beginner and do not want to mess this up with the risk of monthly charges at such a high rate.