Can I connect a RB604 to a RB532 and have full function on all 4 MiniPCI slots on the RB604?

Thanks

Yes, it's work. Tested with RB604 and four additional R52 and R52-350 wireless card.

Will R5H work?

And the new generation radios?

RB532r5 provide 16,5W for extension card. Each R5H max power consumption is ~5W You need check total power consumption and I am not sure about RB532 CPU speed.