Gonna get some raised garden beds, looking for feedback on this plan

So I'm going to get some free raised garden beds and I'm broke. I'll be getting them mid-summer, I know I can get my hands on free horse manure, and I want to do this on a shoestring budget so here's what I was thinking:

1. Fill the beds with free horse manure in mid summer.
2. Get the horse manure to compost along roughly Johnson-Su bioreactor lines without being too strict about it.
3. Add in some rich soil that I can probably get my hands on from a gardener to colonize the horse manure to mitigate the risk of aminopyralid contamination while it composts.
4. Add a fairly small top layer of soil over the horse manure and grow a cover crop like clover or vetch during summer/fall to help keep moisture in and to chop-and-drop to make a good top layer for planting into come spring.
5. While the clover is growing, get some oyster mushroom mycelium going and then when it comes time to chop-and-drop the clover in late fall, lay out a bed of straw and open-cultivate oyster mushroom with the hopes of getting something to harvest but mostly to help colonize the beds with mycelium and to get spent mushroom bedding while breaking down the chopped clover beneath. (We have very mild winters here so oyster mushrooms will do fine with the local climate over fall/winter.) Obviously this will help maintain the moisture of the Johnson-Su layer below as well. The clover and then the oyster mushroom bedding will help make up for the loss in volume as the horse manure layer breaks down.
6. When spring arrives, the horse manure layer will be largely composted and the risk of aminopyralid contamination will be low, and I will have a rich top layer that will be a mix of soil, decomposed clover, and spent mushroom straw that I can either amend or I can dig some of uppermost horse manure into to make it something decent.

I don't really have access to free carbon-rich material as far as I know and I'm not sure if I can source anything for free unless some spoiled hay comes up along the way. I can throw in cardboard waste that I encounter but I doubt it's going to be enough. Any soil that I have access to is garbage and minimal, and I don't have access to leaf litter or anything like that either.

The longer term plan is, to have a very biologically active and rich medium in the raised beds and to leave the horse manure as mostly filler. If I'm lucky I'll be able to get some free woodchips or sawdust at some stage after the spring/summer growing season and I could tear down the beds and fill the bottoms with wood waste, then pile on the composted manure, then grow in the top layer again while the wood waste breaks down from the nitrogen rich, high mycelium composted manure at a fairly fast rate so that I will eventually have really good media to grow in or to use elsewhere.

Anyway, that's my plan to fill up the lower parts of these raised garden beds and to make good use of the space and what resources I have available.

Any thoughts? Is this workable?

(I'm going with oyster mushroom in this plan because mycology isn't my strong suit, oyster mushrooms are very easy to work with, and they'll do fine with paper waste or woodwaste that I throw it at too. I'm fine to diy some carboard spawn for the oyster mushrooms myself on the cheap and I don't have a lot of space so pasteurized straw seems like the most viable option, plus the relatively quick rate of decomposition makes me think that it's the right one for my plans.)