the part I'm confused about is the 'Foundation Kit', with up to 3 slots and the hood with one or two slots. If I get the Foundation Kit can I still put a hood on it?
The "Standard hood" slots into the foundation kit. The other hoods come with the adaptor connector already mounted, with or without filter slots.
The "Universal hood" comes assembled with two (configurable) filter slots, but has no provision for adding vignetting slots on the front (neither has the Wide angle hood).
In which case, do I get the hood without any slots and just use the slots of the adapter. If I get the hood with slots, does that mean I don't use the foundation kit and use the slots in hood?
The foundation kit is only needed for the "Standard hood", to allow connecting to the adaptor ring. The others already come with a connector for the adaptor ring.
My thinking is that the slots in the hood wouldn't be much good for grads since if you twist the hood you could get vignetting. If you use the Foundation kit for filter slots and get the hood without slots, can you rotate the filters without rotating the hood?
The (Linear grad) filters can only be used rotated without the ("Standard") hood attached in its own 2mm slot. All other hoods have the filter holders fixed in place. So you either use the foundation kit with the Standard hood attached or not, or use a separate foundation kit and
a separate (slotted or not) hood.
The site doesn't seem to explain how they all work together.
I agree. The poor availability also makes it difficult to first see the actual things at a dealer, before deciding.
I was thinking of the hood so I could use it on all the lenses and save having to pack three or four shades that came with the lenses. I have the 17-35mm, 24-70, 70-200 (all 2.8's) the 85mm PC (older version) and 50mm 1.4. Sounds like I'd need the separate WA hood for the 17-35 though.
For anything shorter than approx. 24mm focal length, a Wide hood is required, the other lenses should be fine with the non-wide versions. Depending on how the filter mount of the 24-70mm is positioned, a Wide angle adaptor ring may be better for the 24mm focal length setting. For the 17-35mm I would recommend the Wide angle adaptor ring anyway.
I guess I'm looking for recommendation - just the filter slots, slots and hood, or just the hood? What's the most versatile? I have a good B+W CL-PL, (77mm) but I was assuming i wouldn't be able to use it with the system and would have to purchase theirs.
For ultimate versatility, you could get the Foundation kit (which allows to rotate a 'grad' without hood) and a "Standard" hood which can be added onto the Foundation kit. But for the wide angle lenses you'd still need a separate Wide-angle hood to replace the foundation kit. Life usually becomes much easier if you do not use 'grads' but use exposure blending instead, and you only have to decide between a slotted or not slotted hood.
I don't like the straight line 'grad', because the images look fake when used on anything but straight line (horizon) transitions. That's why I use a single slotted hood, mainly for the "Big Stopper", and it can also be used as a hood only (one can optionally remove the slot with a screwdriver if only needed as hood). For optical reasons, I also don't like stacking filters.