It’ll be worth it, trust me. I assume you’ve bought WBP & not standard ply; what thickness did your use?
Use an SBR/acrylic primer.
Generally no. BAL which I use doesn’t recommend it but follow your chosen adhesive manufacturer’s instructions. Flexible powder adhesive only on floors & only use quality trade products.
As before I use BAL, either Rapidset - pot life 45 minutes, grout after 3 hours or if you’re uncomfortable with a short pot life, Single Part Flexible - pot life 5 hours, grout after 16 hours. Check your tiles, some unglazed or polished porcelain tiles require sealing before laying & sometimes again before grouting in order to reduce risk of staining; some tiles come pre-sealed. If they do require sealing, use white adhesive rather than grey on beige tiles.
Grout colour is personal preference but grey goes with practically anything or you can use a darker contrasting colour. Avoid white/light colours on floors, they can start to look grubby fairly quickly. I’d use Microflex but colours are limited. If you want wider choice of colour, Mapei Ultracolour Plus will do you. Mapei adhesive is also good but get the proper trade stuff, not the one sold in B&Q.
