Prop recommendations please: 20' Seafari w/ 150 Johnson OB...

[JUST JOHN]

Hello everyone, as stated, looking (in a panic) for recommendations on a propeller, as I may likely have spun my hub on Sunday. I lost power all of a sudden, and had to troll back the remainder of our journey at 1500 rpm max... above that just "reved" with no forward thrust. I thought this was a gas, bad fuel or clogged filter problem, but after talking to my a local marina on the phone, where the 2-stroke 2004 transom-mounted (stock height) motor was purchased; he keyed me into this possibility. I want to be prepared with some information and brands before heading in to see him tomorrow so I make an educated decision. I'm removing the prop first thing when I get home within the hour, and will update the thread accordingly.

Turns out I have a spare three blade, white-painted prop (aluminum?), I believe I can probably run, but know nothing about it, and really want this boat running again by this weekend! ... and a quick education if you will.

Full recommended throttle operating range is 4500-5500 RPM. The existing prop is a 3-blade right-hand stainless steel unit, with worn black paint; I'll update the diameter and pitch when I get it off the existing one. I always assumed that when we repowered in 2004 that this was the same prop from the original 1978 Evenrude 175hp. I understand that the correct prop puts the engine in the recommended rpm range, and needs to be tested for such, but I'd love a starting point. I rarely open her up, usually cruise at 3500-4500 rpms, rarely over. I don't have trim tabs, and don't really have issues getting on plane.

There's a marine consignment store a block away from my work w/ shelves and shelves of props... bad idea buying used??

Three blade / four blade?

Pitch recommendations?

Brand recoomendation?

Replace with what I have already?

What should I expect to pay?

What not to buy?

TIA

watching this now...
https://www.youtube.com/watch?v=Sp0MdKzXaSw

...and reading through Bushwacker's prop sizing thread:
Propping Correctly and how to test props
Unfortunately I do NOT know whether my tach is accurate!