-new plumbing is all PEX line plumbing-new gas line-new flooring (vinyl click waterproof laminate and carpet in the bedrooms).

PVC, Rubber, Built Up, Tar/Bitumen, Metal, etc...Generally, you'd be looking at somewhere between $4-7/sf in much of the country (and I'd think western Washington should be in that group). 

Given that the property is located in a C/C+ neighborhood with a tenant pool that may not be the best, and with many neighbors owning pets, I'm debating whether to replace the carpet with LVP (Luxury Vinyl Plank) flooring from the outset.I have a cat, and while he's generally well-behaved, there's a chance he might pee on the carpet if he feels threatened by other animals (read: if the other animal is inside the same living space as him).

Remodeling the property- New kitchen cabinets, countertops, appliances, vinyl plank flooring on the first floor and carpet on the second floor.

Would vinyl plank or just some wall paneling be a better/cheaper option? 

We are upgrading with Luxury Vinyl Plank (LVP) flooring, this is an appraisal point and they last longer than the standard flooring, The extras windows (free), granite countertops because once again it helps with appraisal but also last a long time and they check a box for renters, and a few layout modifications that i believe add more value and let the units work better given the site layout.

I have a 16 unit I'm renovating and looking at installing vinyl plank definitely in the downstairs units, but unsure about upstairs units due to noise.

Molding, vinyl flooring under the radiators (only did around them), paint finishes to stairways, finding quality vanities and cabinets that function perfectly.

If you have melamine or vinyl fronted cabinets you are better off doing a door replacement.

No PVC.