I've been finally plowing through this game and I love it.
I put two mods on that really made my life easier and I would think are essential. The easy one was one that puts all your quests on the map. It is a PITA to go to quests tab, move back and look around for what is close by, with this one you can at a glance see what you can do nearby.
The other one I would not skimp out on is friendly hud. It made me use oils. The best feature of this is adding bombs, potions, and oils to the quick swap menu so you can hit RB and just pick your oil, or swap bombs out, or just click all your potions you want to use with no fuss.
Immersive wise what you can do is turn off a lot of hud elements and get a 3d distance marker for the current quest locations and then set it so your interface elements come on screen when you draw your sword or take damage, but if you are in a pinch you can click the l3 button to turn everything back on again.
I had a bit of an issue getting everything going, you have to get the mod merge tool and run it on the mods to use them together. For using friendly hud you need to also turn all the interface elements off in the regular game menu first, then turn them back on via the friendly hud option screen. Really great mod though I wouldn't play without it.
Oh also for play order with the expansions, what I ended up doing was just the main story, heart of stone, and am just starting blood and wine. Heart of stone assumes that the main story isn't done though, so you have to somewhat pretend you didn't finish the game, but it is not a big deal. I think what you could do is play up to the end of the main game, then do heart of stone.
Some people said this makes your char OP for the end but I found once I hit level 30 it wasn't much of a change from 30 to 40 in terms of power at all, even the gear is like, samesy. You can get by the game by dodging and using quen a lot even on the hardest difficulty.
I can't say which order I'd play through if I did it again, I liked sticking with the flow of the main story and heart of stone is it's own entity so doing it in release order might be safest.
Oh yeah finally the other thing that is awesome is nvidea's ansel can take 360 stereo screenshots in game which is just ****ing awesome to look at in a VR headset if you have one (even cardboard or gear vr will work). If you have nvidea stuff on your pc you just hit alt f2 to go into the photo mode and can move the camera around and snap shots, really cool stuff.
Want to talk about the story but still need to get through blood and wine before I open up any spoiler tags