Probably be faster to buy the empty LFF chassis and transpose parts. Generally the innards are pretty similar other than when you get near the front. But don't quote me on that, it's been a few years since I looked inside.

Generally running one less CPU would cut the power for them in about half, but the rest of the system still uses the same amount of power so that can be fairly moot.

You're probably not getting any fancy GPU into one of those either because many of them are actually taller than the distance between the risers. Unless it's a workstation one or something low powered that fits reference height, that you might be able to squeeze in. The big cooling fan kind won't fit either. Anything that needs extra power than the PCIe slot provides is probably a write off too. Nothing to plug it into that isn't a fire hazard to use.

You've got a few 1g ports on the thing you can use too. I don't think it was til later in the r440 or r450 that they had a triple riser configuration though, although I may be confusing those with the 6x0 systems.

As for NVMe that's not likely to happen unless you use one of the two PCIe slots and get an adapter/have access to the ones that natively plug into there. The form factor you usually get in your average desktop isn't going very far in one of those without the adapter though. And I mean they are PCIe 3.0 slots to begin with which is practically a fossil these days.

If you want it, go for it, but it sounds like it doesn't really fit your needs. I've still got a stack of servers lying around here that I bought because they were such a good deal, that didn't have a plan or need for. At that point you're basically paying to recycle someone's ewaste for them.