I had HDR at Mount Vernon 3 months ago.
On day of release, bladder capacity was only about 100ml (550ml before treatment), so peeing often (only just made it home, and had to run in the front door). Over a couple of days, capacity doubled, and has more than doubled again since, so that's not at issue anymore.
On release, I had significant urge incontinence - start peeing about 10 seconds before you expect to (e.g. on the way to the bathroom), and I couldn't feel that I was peeing. The feeling of peeing came back within 2 days IIRC, but had to use pelvic floor muscles to prevent wetting myself on the way to the bathroom. I wore incontinence pants for some weeks and pads for some weeks more afterwards. (I didn't ever let a full bladder go into the pants and pads would have done, but the security of knowing I could pee into them if necessary was well worth having.)
My flow rate halved (25ml/sec down to 11ml/sec) and has not recovered, but is still perfectly adequate. A little of this reduction was down to external beam radiotherapy immediately before the HDR, but mostly it was due to the HDR, a well known side effect.
Initially lost 10% off erection length (was warned before this is likely, and can be permanent), but in my case it has steadily recovered over the following 3 months back to original length. It's because penis bulb (including urethra through it) gets quite a bit of the radiation, and doesn't expand as much afterwards when you have an erection, pulling the penis downward, and it was actually quite painful having a urethra which was too short for your erection, and really heart if you tried angling penis back upwards. No clinicians seemed to have any advice on if I should leave it to rest to recover, or exercise it with erections, but the latter seemed to work, and it's back to original size and pain free now.
3 months on, I don't think I have any symptoms from the HDR other than slower flow.
Good luck with the recovery. I haven't heard of your treatment combination before. What was Jon's staging (TxNxMx)?