I usually wait to switch to the new engine version until a second or third release. If I remember right VaRest should support 4.9 as it is while VictoryPlugin requires an update.
The project is using a modified victory plugin but as long as you don’t do a Linux build it shouldn’t affect you.
There may be bugs in the transition between 4.8.3 to 4.9. I know 4.6 - 4.7 created a ton of bugs. Hopefully there are none! *crosses fingers (If it does anything weird like spawns not working, etc, it’s probably bugs from the version transition.)