I’ve done quite a bit of searching on this topic and found no concrete answers. Will I encounter any problems opening a 3.5.4 project in 4.0.1? I think it is supported and I know I can’t go back once I’ve done it but will it actually work? I really don’t want to rumage through a pile of system exceptions and null references.
Yes.
Things change. There’s no software that doesn’t need to be converted at least a little bit when it upgrades.
If you’re using Unityscript’s lazy-typing, you’ll have some issues. There are some deprecated functions that won’t show up if you don’t have pragma strict, until the code tries to execute them. C# and pragma-strict JS will call out the functions, and they’re easy enough to change.
Nothing that I’ve seen is functionally different, so there shouldn’t be many issues with nulls.
Yes it works. Keep a backup of the 3.5 version, and honestly I’d highly recommend against upgrading if you’re decently far into the project already.