The Snort GUI is as expected. The new Bootstrap GUI for Snort is under development and will be released as an updated package when it is ready. Snort should work OK; it's just the GUI that will look like Snort on 2.2 but with most of the icons missing. There may be some parts of the GUI that don't work properly, but you should be able to use a configuration upgraded from 2.2 successfully.
Your PS/2 to USB adapter will likely be detected as a USB mouse even though no mouse is plugged in. The error related to ums is really only cosmetic.
The pfSense developers are considering dropping x86 support after the last release in the 2.3.x series, as the majority of users have moved on to amd64. This means there is no need for immediate action, but it is worth starting to think about the options for replacing your existing hardware. The chances are that something modern will be more power efficient, giving some sort of payback over time.
There have been some hints that there will be an ARM version of pfSense in the future, but there is no firm commitment over whether this will happen. Additional platform support takes resources, so it may well be that the medium term intention is to use the resources freed up by dropping i386 to support a limited number of ARM boards. For now, if you are looking to buy replacement hardware, you need to look for an amd64 device.