Bear with me for the background or skip to the bottom for the crossover symmetry questions.

I have rotator cuff and impingement problems in both shoulders.  The rotator cuff injury showed up 4 years ago doing front
presses with 40# and 60# sand bags.  The impingement showed itself last fall doing pushups with a 30# ruck.

The combination has left me doing much less and now not doing upper body exercises which has resulted in major loss
of muscle in my shoulders.  After the impingement diagnosis last fall I said fuck it and gave up on doing anything for awhile
and that resulted in more weight gain.  Five years ago I was doing 45-60 minute ruck and sand bagworkouts 4-5 days
a week.  I weighed about 220#.  Now I'm 230# with less muscle and more gut.  I'm 6'2".

I will be 56yo Friday and I know and understand (and reluctantly accept) most of the issued associated with age.

I got a Concept 2 rower for Christmas and started rowing in January.  I'm rowing 5,000m 4-5 days a week.  I think that is
helping the rotator cuff issues, because I can sleep on my side with my arm under my head again.

Last Friday I thought I would try some pushups since the impingement hasn't been hurting.  I did 10 and have had low
but steady pain since.  I need to get my shoulders in shape so I can at least push myself off the ground.

Somebody mentioned crossover symmetry and I have been researching it.  

Questions:

- What weight should I start with?

- I plan to mount them on the wall.  Should I mount them high or low?  I've seen both on YT.

- Are there any recommended brands to look for or avoid?

Sorry, I don't have an answer to your question.  But as someone who put up with a rotator cuff injury for years I can tell you to go get it fixed.  My life sucked because I didn't want to go under the knife but the surgeon finally convinced me that it would only get worse unless it got repaired.  After I was all healed up I started kicking myself for not getting it done sooner.  

Hope things work out for you no matter what you decide.

I'm doing some of the exercises, along with other basic rotator cuff exercises.  I use therabands and cables.  Pretty much the same thing without spending that much money.