Yes indeed, you should make a spoilboard to go on top of the factory supplied baseboard. And yes, a 1/4” shanked bit like the #201 should reach it.
It seems with the z-plus that it does not come low enough to use a spoilboard surfacing bit because the 1/4 shank is shorter.
More importantly it seems that any bit with an 1/8” shank will not reach the additional spoilboard at all. This means you cannot cut full depth pockets or profile cutouts at all with just one additional spoilboard.
The only solution seems to be is to have TWO additional spoilboards on top of the factory board to bring the height up so you can surface the top spoilboard and use 1/8” bits successfully… like when cutting through 1/4” stock which often is needed.
So it seems you need to add around an extra 1 1/2” height to use successfully in those circumstances. This also means that it will reduce the maximum thickness of stock that can be put in the machine by some amount that can’t really be worked out without seeing it.
I hope that Carbide3D will make this clear. Obviously they know all these dimensions and limitations… and should publish on the website to help guide the buyer to the right purchasing decision.
I would like a definitive answer to this from them (@Luke) as I was hoping to buy a z-plus when they become available… but this additional height required has been a surprise and may now adversely affect my buying decision.
I think this issue is only just being noticed because the z-plus is at the moment only going on new machines to typically new users who have not yet realized this shortcoming like the OP and some others.