Which manifold do I need for splitting out wall radiators?

https://www.thetapshop.ie/irish-copper-pipe-vs-metric-copper-pipe/

I used something similar to the one linked in the OP. Flow and return to each rad in qualpex, so no joints under the floor. I installed actuators on the manifold and a thermostat in each room. Works really well.

The only tricky part was connecting qualpex to the manifold. The manifold connections are 3/4" BSP thread, so I had to use a 3/4" FI to 1/2" Compression coupler. Not really a big issue, but it would have been nicer if there was a way to connect qualpex directly to the manifold with a 3/4" eurocone connector. They don't seem to exist for 1/2" pipe.

Should be no problems with those. The will connect directly to copper and 1/2" pex type pipe. Don't forget the inserts with the pex.

I did this recently, manifold in hotpress with 5 rads upstairs and 5 downstairs, rather than the circuits around outside of house, also meant downstairs instead of old pipes coming out of the ground with multiples bends to line up with radiator they just come out of wall direct in to the rads so much neater and cleaner floor.

A lot of the manifolds are for underfloor heating and are designed for having actuators. I went with simpler ones like this https://www.heatmerchants.ie/x-iso-valve-3-way-heat-merchants-pro-manifold-u42100 they have a valve but more for just turning on and off, was handy for filling system after replumbing as could just open one at a time. Got 4x 3 port and 4x 2 port to make 4x 5port, upstairs and downstairs flow and return, then pipes with no joints to the rads (there are some joints in mine as for some I finished with bit of chrome pipe but no joints are required). TRV's on all the rads then to control room temps, looking at getting some smart ones now shortly.

I just used standard qualpex and compression fittings, I did look into some of the fancier ones and Hep20 a bit but I can't see there being any issues with the standard qualpex, that said I'm not a plumber so don't have a lot of experience

The 4 x 2 way and 4 x 3 way, which I needed to make up 4 x 5 way cost 128, they are 3/4" BSP in and 1/2" compression out.

The ones I got are slightly different to the ones on the website I've attached pic, you'll want end caps for them also as open at both ends, can't remember what they cost, few quid. I used pipe thread seal on the threads to join them, you could just use ptfe but I kinda prefer the thread seal over ptfe as always bit unsure how much ptfe to use to get seal I think the thread seal is bit more amateur friendly but best do your own research and decide.