Any liability I can avoid by having them install their own units?  

New roof, solar, paint, lvp in the living room, granite countertops, cabinet handles, fixtures, carpet on stairs and upstairs, refurnished entire house.

Found some good contractors, painters, floor installers, that I've already recommended to people and will again if you ask.

Trying to estimate total cost to install new vinyl plank flooring throughout.

I just installed keyless entry.

You absolutely can use an installment sale in conjunction with a 1031 exchange... though I’m not sure if this is the answer to the current predicament.. we handle these all the time, especially on straddled year 1031 exchanges.- REI CPA

For example, it cost a lot more to install quartz countertop then laminate.

We just installed a eufy, it works great remotely as well as for guest. 

Who are your preferred french drain installers and plumbers/ HVAC contractors in north jersey?

A new cooktop/oven range and slide-in refrigerator is part of this project, as are replacing laminate countertops and installing a new sink and faucet.