B78XH VS pms50-gns530

Heavy-Division's 787 improvement mod (git)

Look for yourself, features listed: https://github.com/Heavy-Division/B78XH

Download the Heavy Division Mod. It may help some of your problems while adding more realism.

Heavy Division 787 - GitHub

It's the same here, for the one plane, you should check out this: https://github.com/Heavy-Division/B78XH

To be more serious about your autopilot/garmin question, this uses the ASobo AP and Garmins, though you can improve those with free/paid mods and the plane supports those too. eg the GTN750 from PMS or this GN530

I suggest getting this mod. It adds a lot of RL functionality.

Only for the addon 430/530, but the instructions are on the GitHub. https://github.com/pimarc/pms50-gns530

PMS50 also has a GNS 530 mod that adds more features too. https://github.com/pimarc/pms50-gns530

Also if you don’t have it, grab PMS50’s mod for the 530/430. It brings it much closer to real life function/less frustrating. https://github.com/pimarc/pms50-gns530

As others have said, X-Plane is probably the best bet for instrument training, although it depends on what instrument systems you are trying to learn. Steam gauge VOR/ILS works great in MSFS in the steam gauge planes so you won't have any problems there. If you will be using a GNS530 or similar, there is a great free mod for MSFS that adds a good implementation for those systems: https://github.com/pimarc/pms50-gns530 The G1000 today is still severely lacking even with the Working Title mod, so I can't recommend it for trianing.