I took Philosophers Stones two times, first time, 10g of the lightest (according to smartshop's advices) and it was great, pretty visual and confusing trip ("What the fuck am I doing here ? :O"), the second time 15g of Golden Teachers truffles, on an empty stomach, it was great too, hilarious and so.
The smallest dose they sell you (in Netherlands) is 10g, I think it is the best dose you can take for a first try, because indeed, it can be very surprising.
I never took alcohol while tripping on truffles, because I wanted to feel precisely the effects from the substance I was taking, with no parasites feeling, but I think a couple of beer won't destroy you or your trip. More... I couldn't say what are the effects but, juste, be careful mates.
Have a nice trip, and because it is never said too much times : good Set&Settings is very important and can totally change your trip, take care of it !
PS : I didn't understand it the truffles are rotten or if you fear they rot soon, but indeed if they are rotten, forget it ! And eventually, if you want to conserve it, just cut it in slices, put it between two sheets of paper on a radiator and wait +/- 2 days, I used mine two months later and they were still good ! (I took it in a cup with hot water)