The brakes are not great but if they are really bad there has to be something wrong. It also depends on what tires you use on the bike. On my bike I use MT21 and there is no problem to lock the front wheel in 120 km/h, even when I drive with luggage. I’ve also used TKC80, Avon Gripster and it gives the same result. With a more street oriented tires it might be different.
This winter I changed to a metal braided hose and the feel really improved. Off course I still have to use force on the brakes but that’s not a problem as long as I know what’s happening and I know that you can lock the wheel if I have to.

When it comes to the forks I also rebuild them this winter. After a lot of thoughts I decided to keep the bike “low” and keep the original fork-legs, mainly because I didn’t want to lift the rear and stress the shaft. So I mounted inlets (the same as HPN sells but Q-tech are cheaper, BMW also sell them).
There is still a lot of snow on the gravel roads around here so I have mostly tested them on tarmac but they feel good. It should be interesting to test them further, to try other springs, adjust them and play with the oil-level.

Rebuilding the forks is not an easy task, and the first thing to do is to know how you would like the forks to handle. All springs are different and IMHO you are lucky if you buy something without research and it fits your need…. The same applies for the hydraulic.
If you have a PD tank it will probably come in conflict with a 50mm setup. The same goes for indicators, dashboard and so on…

IMHO it’s not necessary to strengthen the frame if you don’t change the suspension to much.

BTW a friend of mine has mounted a shortened Magnum-fork on his old G/S and increased the ride height a bit in the rear. It will be interesting to see how it works when he has finished the bike.