Yegods what a lot of frikking twaddle
Steering stops at 80 quid worth every penny?
Do a search here and you'll find a very effective steering stop mod that will cost you nothing, or at most , a few quid for bits.

(Basically a couple of knobs from a TKC attached with cable ties)
Tourtwat steering stops are for posing nancies who turn up at the ACE cafe with full but totally empty panniers, wearing the latest twat suit and post ride reports up of their latest franticly awesome big trip down to Brighton
If you are going to ride on rocky stuff, losing the screen may be sensible....otherwise, just loosen things off a bit and it will give enough 'squidge factor' to get away with 95% of falls.
I have NEVER seen a handlebar lever getting broken on a GSA, and I've never had a problem with he bog standard hand guards either.....they do the job well....I HAVE seen a gear change footlever get snapped off on more than one occasion though, although it hasn't left the bike stuck, just hard to ride.
(I've just fitted a Touratwat extendible change arm, mainly because I have feet to match Shep's barge and with my offroad stomping boots on and pivot pegs fitted, I couldn't change gear effectively, if at all)
Pivot pegs by the way, nice, comfy for standing up for a long period but not high on the list of priorities for Offroading a gs)
Get a grille over your lights...that glass is expensive and it only takes one roostering from a mate ahead of you to crack them.
Get rid of the stupid TUV rules plastic bump guard off the rear end.....it can easily get caught up and dragged around the wheel.
A 21 inch front is nice, but the standard one will do fine.
If you're going to get offroad with luggage/pillion, get a couple of fillets of strengthener put in the frame around the rear subframe joint.
A gel battery is safer when the bike is over on its side (or further, which often happens when riding ruts or rocks) as it wont be pissing acid out, and will e less likely to throw a plate and conk out totally after a good few hours of shaking about
Suspension......definitely upgrade if you can...you can put some of that £80 I just saved you towards that
I wouldn't bother with a smaller tank either tbh......if you can find an old tatty one, bung that on and
just don't fill it up as full!!
The weight isn't in the tank metal, its in the liquid contents, so that's another few hundred beer tokens saved
Mirrors.......leave on, just make sure they are a fraction loosened.
Crash bars yes, definitely.
Steptoe head guards yes, if you can find a set, or (and it sticks in my throat saying this ) the touratwat head guards...you should see the state of mine after 7 years offroading in Morocco

but I haven't cracked a head yet
Bash plate yes, centre stand fill-in bash plate yes (best used for sliding over rocks rather than getting stuck ON a rock)
Clocks? No need to change at all, unless this an exercise in posing rather than functionality...get a decent GPS and a RAM mount and that will give you all the data recording that you need, plus on most now, you can load up OS maps or TOPO maps for many many areas
Get a decent, light but sensible toolkit sorted out....chemical metal and a tampon will fix a holed head, cable ties and gaffa tape can strap up a broken frame securely enough to get out of a sticky place (been there done that

) and a couple of long thumb-catch webbing straps (available Gratis from your local BMW Mottorad if you ask nicely) will pull a bike out of a watered rut or out of a deep hole, or even tow a dead bike home
Gaffa some long tyre levers to a frame member, and take some rat-tail type puncture repair stuff and a cheapo Halfords bike pump cable tied on somewhere.
The lights on an 1150 adv are weak, and no good for the slow gnarly stuff that you may one day find yourself stuck on at dusk.
We've come down out of the mountains past midnight before now , even though we planned to never let it happen...sometimes, shit just happens, and you'll really appreciate some extra lights....even cheapo fogs will illuminate the ground drekkly in front of you so you can get down tough stuff, and an HID main in the forests will mean you can make sensible progress after the sun falls (a good head torch is handy as well, for many reasons)
(Don't even consider the OEM BMW fogs for anything more than being on tarmac....they have brackets made of chocolate plastic and are guaranteed to snap the first time your bike takes a rest

)