Which Mac for my editing needs

A mid range Macbook Pro 16" or iMac should do the trick

At least a 2.4Ghz CPU with 16gig RAM should give you decent results.

You want blistering speeds get the Mac Pro and pump in 512Gig RAM with 2 Vegas

Thats should fly through 4K 

Mo

Since most of these clips are shot using a h.265 long GOP codec, this is quite taxing for any editing system.

h.265 really is a delivery codec, not an editing codec.

Due to the way encoding is done, it requires a lot of processing horsepower to show a single stream, let alone 7 of them, I presume, in a multicam sequence?

Here's more detail on how to work in a multicam sequence: https://helpx.adobe.com/premiere-pro/using/create-multi-camera-source-sequence.html

Better approach would be to transcode the clips to an edit friendly format first, such as ProRes 422, or let Premiere Pro create proxies first. Although I'm not sure if or how proxy editing works in a multicam sequence.

Here's how proxies work: https://helpx.adobe.com/premiere-pro/how-to/proxy-media.html

As to which Mac will be sufficient for editing, please check this list: https://helpx.adobe.com/premiere-pro/system-requirements.html

Hope this helps.