I only have the MW 1000 extension table, not the cart (as it dosn't fit well into my car).
Have looked at it at close though, given your description here's my advice:
You can have several systainers (depending on size) on the MW 1000, the height of the drawer is adjustable and it can be removed completely in case you don't need it. The small (fixed) table ontop seats a systainer (there are groves for the feet) without it slipping off, though it's not locked and you'll have to keep in somewhat upright position - see video below.
IMHO: As it's easily moveable with the extension table stored in the back and setting up/packing the extension is a quick process when you know how it works... when you need the extension table as highly mobile workspace and have the space in your van - you should get the set.
To move more systainers:
When needing a vacuum anyway: A CT can (within reason) also stack systainers.
A sys-cart, as alternative to a sys-roll, isn't that expensive (at least here in europe where we have a free market for festool dealers), it's OK to use on somewhat even floors (=inside buildings) and can be controlled well enough (when not been stacked too high) using the handle of the top systainer. On stairs you'll likely have to disconnect the stack in the middle and carry with both hands, a sys-roll might be better when there's no elevator. Sys-Roll also has the downside that you can't open a T-lock stack in the middle, so for a mobile workspace (opposed to just transportation) it's more suited for the SORT/3 and other drawer systainers.
With careful selection of the systainers to put on the CT and the sys-cart/roll you should be able to end up with the same height as the MW 1000 (same as MFT/3) should you need to support long workpieces.
an impression on systainers on the MW 1000 and moving it around.
My experience (when needing to move more tools) is that it's better to move two smaller stacks than one too tall one. Also keep in mind that having several stacks means that you have several top systainers with instant access (without having to de-stack or hold the upper systainers to keep them from breaking the lid) at a convenient height.
It all depends on what you actually need to bring, knowing that in more detail could give a better answer.