Quarkrad

I have done a lot of work (too much wife says) preparing to tile bathroom. I have built stud wall for corner shower unit (one wall **** panel one brick/plaster) and ordered Dunlop tanking kit to seal. My walls are a mixture of existing tiles (cleaned, taken out loose tiles and filed with new plaster), 2.5 sq m of new plaster and existing plaster walls with old wallpaper stipped off. Appreciate it would have been ideal to take off old tiles but for reasons I will not go into they need to stay on. The walls are clean and ready to go (tile) but I have doubts. I am happy about the shower area as I will put on primer and the waterproof layer from the tanking kit but what about the rest of the walls? Advice seems to be keep the existing tiles clean to tile over but various opinions about the other wall. For the new plaster should I put up some bonding/sealing poduct before I tile? And do I leave the existing, wall paper stripped, walls alone? Some say bond/seal with 2:1 PVA but I can see the arguement others say about breathing and never touch PVA. Any advice on final wall preparation much appreciate.