Here you go.

Often a little grinding PLUS a little levelling compound and you are good to go.

When removing planks that have been installed, you must be VERY careful. The click edge is VERY fragile. Slow and steady wins the race. If you are careful, you might take the same amount of time REMOVING the floor as you did installing it. It needs to be VERY CAREFUL.

Be prepared for loss of as much as 25% (that is a 'worst case' scenario but it is not unheard of). I HIGHLY recommend you pick up a few more boxes (this is to ensure you have the same batch/dye lot etc) just in case.

Take your time. Vinyl is VERY persnickety when it comes to removing and reinstalling.

Is there a noise abatement that you must achieve for your condo? Wood frame buildings usually have noise abatement requirements which vinyl isn't always up to the task. Have you checked with your HOA/condo board.

Thanks so much for the detailed advice, @SJ McCarthy! I do have 3 extra boxes and then some, and so far pulling them up isn't seeming too difficult to do but I'm sure we'll run into some issues :-)

The condo rules aren't very specific: 80% of floors must be carpet or area rugs - we have carpet in the bedrooms and someone on the board told me that LVP with an underlay is fine; this one has a pre-attached pad. But thanks for brining it up - I do want to run it by them once more to be sure before we totally finalize things.

When you say "a little grinding PLUS a little leveling compound" are you referring to self leveling compound? It does seem to me that SL would be the best way to easily get a good level. We've worked with some patching material (Henry 345) on a few spots, and it has the appeal of potentially being simpler than SL up front (doesn't have to be mixed and doesn't require primer), but it's more expensive for covering a given area, and doesn't level itself.

I'm still trying to figure out if we can reasonably apply self leveler to just a portion of the room, and I'm thinking mainly that will require that there is indeed a consistent "low" spot / sink so that the SL doesn't run out into the areas we don't want to repair. That does seem to be the case, but I need to really spend the time with a level to fully map it out.

Thanks again!

You will need a 10ft level or a laser level to figure out what your subfloor needs to achieve the levelling requirements of the flooring.

By grinding down the high spots (a few mm in each spot) and levelling the low spots you can achieve flatness. A 'level' floor is different from a flat floor. The flatness rating (printed in the installation instructions) must be achieved.

Your level of competence will dictate which product you use. You will also need a smooth finish (don't want bumps and lumps).

The amount of work you put in will be up to you. How much do you 'mind' a bouncy clicky floor? How much do you hate a floor that moves up/down every time you step on it? Will you accept more issues just because it is DIY?

I can't answer those questions. Only you can...because you are the one to live with it for the next 7 - 20+ years.

Following up on this again as I'm getting ready to actually dive into this project after taking time to gather advice and get a better feel for where all the issues are.

I was initially leaning toward just using Henrys 549 feather finish (thank you @G & S Floor Service!) but have had several people recommend 1/4 plywood so that's a contender also.

I've also done more measuring and found that at the main entrance to the room where i'd originally noticed the biggest drop, the drop is roughly 1" over 4 feet, which from my understanding is quite substantial. I'm attaching an image of where this is, along with the second biggest issue which is a local low spot. The latter seems like a very straightforward fix with the Henry's 549, but I'm wondering if that 1" drop is over my head or might even require some work on the floor joists or something (which I assume I'd need to get the owner's association involved with).

I'm wondering now if it would it make sense to fill in the local low spot (and other more minor low spots) with 549, and then add some 1/4" plywood everywhere except for the area marked high, up until say a couple feet out from the drop, then ramp up to the high area using the 549 or something, so that the incline is less extreme? Or if anyone has other suggestions for how to approach this they would be quite welcome!

Thank you!!

Is the 1" drop from the high spot to the opposite wall? Or is there a step there?

@G & S Floor Service Sadly it's not a step, just a fairly quick decline down from the high area along the line of arrows I drew there (it slopes down from the wall there and continues in a line out from the wall across the entrance to the room)

If, you want to bring the 1” up to level. Fill all the low spot with as much plywood and shims as possible To bring up to 1/8“ of your height. Then finish off the final 1/8” with primer and self leveler to bring level and flat.