Hiya,
And Welcome Aboard
With the steam version you're missing out on being able to fix a multitude of things (you can't patch steam .exe)
You can start by getting to grips with tdw's newui's, in there you have options for settings from advanced hud to sh3 style
There's a few other ui's that will maybe tickle your fancy regarding being more like sh3
Not being a steam user myself, no doubt a 'steamer' will be along to help you out
Have a scroll through the two main sh5 forum parts, you should see ideas from other steam users that have migrated from sh3
DBSM is here, so maybe read up on that
There's gotta be many things here that you should recognize, just browse and read i guess
Sorry i can't be much help
TTFN