I don't think there is any way you should add more than 10%. Manure varies. The stuff sold in AZ in bags as steer manure is from fedlots and I would use very little. Very salty and really not such great stuff. From a horse stable with lots of bedding and allowed to compost, 10% might be ok. I have use up to 30% aged composted yard waste in heavy soil with no problem. The garden soil and potting soil sold in the state is very heavy on logging waste ie composted shreaded bark and tops. I have worked over 50% organic compost by volume into native AZ soil over a couple years.

This is my own horse manure with some nice sandy dirt mixed in. It's been composted for about 6 months. No bedding materials like shavings, weeds shouldn't be a problem as the alfalfa is very clean. Maybe a few errant flax seeds but who wouldn't a few flax to attract bees to the garden?
I also have tree shreds I would like to use for mulch. Some green, some browns. And a bunch of coffee grounds.
Since my water I ground soil is alkaline should I add some gypsum and sillier like I do my in ground garden? If so, how much? Anything else? Alfafa meal, bone meal?

On the previous post I meant to say sulpher, not sillier. Gotta love the auto correct function!

I've used lots of composted manure before. it depends on what you're going to grow. Some plants thrive on nitrogen, cucurbits for example. Others are sensitive to too much nitrogen.
If it's been composted for 6 months, I wouldn't care. I've totally filled a couple of my beds with manure (I don't know how much it had been aged). But here nitrogen tends to dissipate pretty fast out of the soil. The heat and the sun do that. Even if your plants don't do so well the first season, by the next season they'll have no problem, and using composted manure is a heck of a lot better than this hard clay

1/3 soil 1/3 sand 1/3 manure.

Well, so far so good. The basil really likes it. Haven't tried the cucurbits yet. I'm thinking about a couple of rows of corn for shade.