B5 speaker upgrade...few questions!?!

[Prism]

Im looking to upgrade my speakers from the standard (which sound like they have maybe blown a bit) to a set of Rainbow component speakers for the front and looking to purchase Alpine component speakers for the rear...

I am struggling to find a definitive guide, but I have read that "spacers" might be required ? Is this the case and does this cause any issues with put the door car back on with the original speaker grill ?

Also is it true that they are riveted in, so will required to be drilled out ?

Finally I have read that it quite hard to find somewhere within the door for the crossover ? any confirmation on this ?

I have searched already and finding lots of different answers (which some are confusing me a little). I would prefer just to know what to do before I start to it myself as looking to change this asap.

Thanks in advance

Rob