Please do not report multiple issues in one report. This just makes handling them much more difficult.

That being said, you can continue to use the 32-bit version of OpenMPT on your new machine. In fact, that is exactly what the download site recommends you to do if the majority of your plugins are 32-bit plugins. Your second and third bullet point are known issues already covered by other bug reports or cannot be solved at all. This means only point 1 remains, but I have never seen such a behaviour with the plugins you mentioned, so I will check it out later in case anything changes in those plugins.

To give a short explanation why the third point is a known issue that cannot be fixed: Bridged plugins run in their own process, and their UI is not directly embedded into OpenMPT's plugin window like non-bridged plugins are. It only looks as if they are, but they are completely separate. Not all plugins allow for keyboard messages to be passed on to OpenMPT in this case, which is why not all bridged plugins allow direct note preview. With many other plugins it should work as expected, though.

So if i have a problem with the GUI elements taking focus away, the solution is either don't use those problematic 32-bit plugins on a 64-bit machine (if i want the same response and behavior), or use them only in 32-bit machines, if i understand your resolution correctly.
Could it be a problem with the bridge? Might other 32-bit bridges have different capabilities or problem-solving methods? I don't haveany problem trying others.

Concerning the volume being reset after stopping playback, i thought i had seen it occur on more than just the Zebra VSTi's. I will test my others as well, to see if it's a problem with VSTi architecture or versions, or if one of openMPT's settings is triggering the reset inside certain VSTi's.

As I have explained before - you can run the 32-bit version of OpenMPT on a 64-bit machine. If you use lots of 32-bit plugins, this is the recommended way to go. In such a scenario there is little to be gained from running the 64-bit version, but the 32-bit version will still run way better than OpenMPT ever did on your previous 32-bit machine (for the same reasons I explained already a while ago when you asked a similar question: 0000923:0003223).

Could it be a problem with the bridge? Might other 32-bit bridges have different capabilities or problem-solving methods?

It is very well possible that these specific would work better with jBridge, as there is lot of undocumented black magic happening in plugin bridges, and I certainly haven't figured out all of the tricks that jBridge pulls off to bring OpenMPT's bridge on the same level. jBridge isn't free, though. There is a demo version to try out, though.

Concerning the volume being reset after stopping playback, i thought i had seen it occur on more than just the Zebra VSTi's. I will test my others as well, to see if it's a problem with VSTi architecture or versions, or if one of openMPT's settings is triggering the reset inside certain VSTi's.

I certainly cannot reproduce it here, but since there are many ways to change the volume in Zebra, maybe I'm just trying something completely different than what you do.

Fortunately, the Zebra plugins have 64-bit versions so this irritation can be put aside...

Closing as no additional information was provided.