Outside render wall

I would only advise that you coat the wall with a 70% PVA & 30% water mix to seal the wall to improve suction and extend your drying times. The only boarding to consider is if you want to insulate the building from the outside with kingspan or cellotex in which case you would have to fix EML sheeting over the top for the render to key in to.

I agree with elexitwch. Blocks are extremely porous and therefore will dry the render too quickly leading to cracking of the render. A Pva/water mix will seal the blocks allowing the render to dry at the correct pace. No news to board

You don't need to do a board on brick or block wall before rendering

You can use a product called blue grit or sbr to prepare the wall prior to rendering . Also make sure you get plastering sand to make the render .. You might want to mix a waterproof agent in with the render to add better weather protection ..

You should coat the wall with SBR. I have seen previous answers stating to use pva, but this must not been done on exterior walls. It is fine for sealing internal walls but pva is still water soluble after it dries so if moisture gets anywhere near it, your seal is gone. SBR creates a permanent seam and will keep your work on that wall for many years to come.