Coco has a lot of advantages, but I'm worried about you don't have any coco specific nutes, on the other hand if you go slabs you'll need more expensive trays.

I mix (not in the same batch) hydro and coco nutes, it works fine for me.
They say you have to use only coco nutes with coco, but they say a lot of things.
I think I know what I'm doing

So get slabs and trays or coco and some coco nutes.

You'll still be able to use your DM, I'd like you to have some coco nutes on-hand though, in case a prob with going DM in coco comes up.

Getting a grow under you're belt is the most important thing at this point..

You can get going w/ the DM and get some Canna or H&G coco nutes by mail later.

IDK, you need a plan, Stan.