Replace a tired roof before the array, not after
Panels outlast most roof coverings. If yours is within a few years of the end of its life, replace it first. Removing and reinstalling an array to get at the roof underneath is a cost with no offsetting benefit whatsoever, and it is entirely avoidable while you are still quoting.
Ask for a condition assessment rather than an age estimate. New Jersey roofs go through freeze and thaw cycling as well as summer heat, and a covering can be closer to replacement than its age suggests. Consider getting that assessment from a roofer rather than only from the company selling you solar.
Ask how many layers of covering are present and what the structure underneath is, and whether anything needs reinforcement to carry the array. An installer who has not been on the roof cannot answer those questions, and the answers change both the price and the design.
If the roof does need work, coordinating both jobs is usually cheaper and less disruptive than doing them years apart. Ask the roofer and the installer to talk to each other about sequencing and about how the mounting will interact with the new covering.
How it attaches, and who stands behind it
Ask how mounting penetrations are flashed and sealed, and what method the roofing manufacturer approves for your covering type. If the roof is still under a manufacturer or builder warranty, establish the position before work begins rather than during a future claim.
Ask what the workmanship warranty covers on roof penetrations specifically, for how long, and who honours it. This is the warranty that matters most and it is the one people read least, because the failure it covers arrives years after everyone has stopped thinking about the installation.
Establish who honours each of the other warranties too. Panels, inverter and workmanship are commonly covered by three different parties on three different terms, and a company that has left the market cannot support a workmanship warranty however well it is drafted.
Get equipment specified by manufacturer and model number rather than by description. Model numbers are what make a warranty enforceable later and what let you compare two quotes on the same basis rather than on adjectives.
Production drives both revenue streams here
New Jersey provides full retail net metering, crediting each kilowatt hour your system produces over the course of a year, and the Administratively Determined Incentive pays on generation, with one SREC-II created per 1,000 kilowatt hours and a guaranteed term of 15 years.
Because the incentive pays on generation, the production estimate drives both revenue streams at once. That makes it the assumption most worth testing, since an optimistic figure inflates the projected result twice over rather than once.
Ask whether the estimate was modelled for your specific roof, orientation and shading rather than a regional average, and ask for a shading assessment covering the whole year rather than the hour of the site visit. Orientation is the decision that most affects output and it cannot be recovered later with better equipment.
Confirm a separate Solar Production Meter is part of the installation. New Jersey's Clean Energy Program states that the metering used for netting and crediting cannot measure gross generation for REC or SREC creation, and that relying on one meter for both would leave the customer-generator short changed.
Two exemptions, and neither one happens by itself
New Jersey exempts solar energy equipment from state sales tax, but the exemption has a procedure and it happens at purchase. Under N.J.A.C. 18:24-26.4 the purchaser must issue to the seller an Exempt Use Certificate, Form ST-4, or other approved form, indicating on its face that the purchase qualifies for exemption as a solar energy system, with the installation property address inserted.
Ask your installer how that is handled and confirm the certificate was issued rather than assuming the price you were quoted already reflects it. It goes to the seller as part of the transaction, not to the state on a return later.
The property tax exemption is separate. Qualifying renewable energy systems are exempt from real property taxation under N.J.S.A. 54:4-3.113a to g, but Form CRES, the Certification of Renewable Energy System, must be filed with your local municipal tax assessor, and the system must be certified by the local construction code official.
The annual exemption is the difference between the total assessed value of the property before and after the system has been installed. Nobody files Form CRES for you by default, so ask whether your installer assists and put it on your own list either way. Requirements vary between municipalities, so a short call to your own assessor asking what they need is worth more than any general guidance.