Is the clamp a crimp clamp?

No. Clamp comes as pictured. It is not a crimp clamp.

Can this be replaced on a N20 without draining all the coolant?

You don't drain all the coolant to replace this flange. You will lose coolant when this hose id disconnected. Easiest/mess free way of dealing with this is to drain the radiator slightly.

What is the proper PN for the hose? I had to cut the hose on my old plastic flange off my other car but want to replace the entire hose this time on my other N52. I believe it is 11537545890 but just want to confirm? Thanks!

We need year and model information to confirm the hose for your application. For N52 applications there are 4 different hoses depending on the chassis it is installed in. If you enter your year, make, model into the vehicle selector and search "mickey mouse hose" you will get a result for your vehicle. In some applications the hose already includes the aluminum fitting from Rein pre-installed. You will see a standard option and upgraded option.

Can you tell me what part number the rubber gasket is? I pinched it when installing this piece and I need to order a new one...or two.

Please see p/n 11537545278.

what do i have to cut ? the hose or just the tight metal clamp thats around it ??

You need to cut the clamp. There is no other way to remove it.

How do i remove the metal clip of the old hose ? Thats the only challenge i have

It needs to be cut off.

Does this include the o-ring or do I need to order separate? Description only mentions the clamp.

The o-ring is included as seen in the photos.