Few questions for a United noob. I read through this thread but it is very confusion when the upgrade gets PQM/PQS/PQD.

I have a $100 United voucher and I am looking to use it for a paid upgrade before it expires. Is this allowed?

I don't need PQD but am interested in the PQM as I am doing the Premier Gold status match challenge. How can I tell if the upgrade will earn the PQM?

From the United app or website I can see an option to upgrade. Do upgrade prices fluctuate and how do I get the best price that earns PQM's?

Current upgrade prices:
Phoenix, AZ, US (PHX) to Raleigh/Durham, NC, US (RDU)
$139 / person PHX to SFO 2 hr 0 mn Airbus A320 United First
$259 / person SFO to RDU 5 hr 10 mn Airbus A320 United First

Raleigh/Durham, NC, US (RDU) to Phoenix, AZ, US (PHX)
$169 / person RDU to IAH 2 hr 55 mn Embraer ERJ-175 United First
$179 / person IAH to PHX 2 hr 41 mn Airbus A319 United First