What bullet weight/styles did they like?
124 gr loadings are the most accurate in 9mm CZs. It may or may not like 147 gr loads, depending on the ogive of the bullet. CZ chambers conform exactly to CIP specifications, so there is no extra room near the leade for the larger 147 gr loads to "cheat" into.
How does the recoil compare to other guns (specifically the USP 40, Sigma 9VE, Glock 27, and 97B)?
It's a 9mm. Recoil is very slight. It is a heavier pistol than the polymer models you name, and the PCR shoots a lot "smoother." If you like your 97B, recoil will be a non-issue.
What alterations have you all done to yours?
In general, I do not advise going hog wild on modifications at first. I have owned a grand total of about a dozen modern CZ pistols over the years, and I currently own six (excluding Dan Wesson). The most I have ever done to one was change the sights AND the grips. The PCR comes with WAY better sights than the average CZ 9mm, so that's a non issue.
The problem with modifying CZs is that usually people are trying to make an equipment fix on something that doesn't need it, or a factory model already had the desired features. For example, the vast majority of people who feel the need to hot-rod a 75B would have been better served by an 85 Combat from square one. Also, you will not see any return on your money should you sell the pistol. (It's hard to sell a used pistol when the brand new ones are still around $500.)
Who uses the SS guiderods?
Not me. You gain nothing by doing so in this model, and the issue delrin guide rod is much easier on the barrel shank, according to CZ-USA's chief gunsmith.
Should I buy an increased power spring, since it will be my carry pistol and will see a decent amount of +P?
You might pick one up to try, but I doubt it will be absolutely necessary. The OEM springs in a PCR or P-01 are quite strong, unlike the OEM springs on the 75 Compact. Go figure...
I would have several PCRs if they came with a manual safety like a 75/85 series pistol. That is the only real downside of the PCR. In terms of the overall features and price, I like the PCR better than the P-01. The 75 Compact has the manual safety, but it is almost as large and heavy as a full-sized 75B.