In Germany the MSI Trio 3090 is at about 1900 € on preorder. so, the price you found wasn‘ that bad. Some online stores have the Zotac 3090 on stock. All other‘ s are still on preorder.
The Asus ROG 3090 OC is now at about 2050 €. I don‘t know if any customers got one so far......seems to be one of these miracle treasures people looking for but never find.....
I use my old flightsimPC i7 6700K 16GB now as client PC as well.
I have Littlenavmap and ActiveSky ASPD5 RC1 in network configuration with my flightsim pc.
My plan was to run REX Skyforce on the client, too. But this doesn‘t seem to work in network config. Only the weather engine is configurable for networking, not the rest of the app.