Good morning! (Well it is here in the UK!!)

I also have a 5DS-R and an EF70-200 f2.8L IS II, and here's what I have learnt. The 5DS's high resolution put high demands on lenses and user and it shows up any weakness. I also learnt that pixel peeping can be depressing verses reviewing a printed image for normal review. But overall, I'm staggered at the image detail this camera and lens combination can achieve.
Practical things I've learned with the 5DS-R:-
I use the silent shutter mode to help reduce shutter vibration;
Use the back button for focusing, personal thing, but for me seems to aid a smoother shutter press;
I have also invested a good tripod, something else this combination, due to weight/size and resolution, demands.

Another element in this thread, is the live music, I also enjoy taking pictures at local music events, normally unsigned cover bands in local pubs where the light can be terrible. For this I enjoy the 16-35 f/4 for the wide angle if not the f/4 limit and the 24-70 f/2.8 helps with focal range and low light, but my favourite lens is the Sigma 50 f/1.4, which works well in low light and provide a great DoF to pick out an individual, although focusing in low light with the Sigma is often a slower affair.
I've also got over worrying about high ISO and Noise with the 5DS-R, especially with live music. Yeah sure, if you Pixel peep - loads of noise! But I'm sharing images with unsigned bands, who are really pleased. Not once have I ever had "that's noisy" - I have occasionally had "I like the grain!!!"

No real advice in my post, other than try to develop a rock steady technique and be less sensitive about high ISO Noise!

I'm still learning, and this forum and resources have been a great help over the years.

PS - Happy New Year!