I would speak to at least 3 and it's not something I would skimp on, at least upto and including RIBA stage 3. After that, it depends on your experience and your builder.
also this, I think being so painfully millennial I always chose 'services' that are on internet rather than physical. I made this mistake with my accountant too. IRL/trad high st/local is so much better in terms of experience.
I would speak to at least 3 and it's not something I would skimp on, at least upto and including RIBA stage 3. After that, it depends on your experience and your builder.