I bought a bracket for our D850 (can't help you whether you can source one for a D500). It was about a 3rd the price of the really expensive ones.
First I tried a generic one but it was hopeless. Then I found a better one that cam with the correct openings for the D850 and the base had an uplift on the back which the camera fitted into. So now the camera fits snugly into the L bracket and because of the uplift it cannot come loose which is the bugbear of all mounting systems. I would not touch generic with a barge-pole now especially since the generic DON'T have the uplift.

I also have an extensive Manfrotto tripod and head collection. I have just finished converting everything away from their QR system to Arca-swiss. There were a few things to learn but the three main points to watch for are that you should take as much use of the 3/8" fittings as possible. These are generally found as the top bolt on the tripod or the bottom thread on a head. All my AS fittings came with the 3/8" to 1/4" adapters so just a case of removing these.
The second thing to watch for is that some of Manfrottos heads come with a special fitting which is keyed to the bottom of their QR clamp. So if you remove the clamp you cannot fit an Arca-swiss fitting onto the head securely. Now if you look at the bottom of a generic AS clamp fitting (I used generic for all of mine) you will notice that there is a cutout either side of the screw hole. I used to wonder why this was so but about 2 weeks ago I found the adapter which keys them both together. I have only ever seen one supplier that has these adapters and I am waiting for two to arrive any day now. Only a few dollars for a pair.
The last thing to watch for is that I had a lot of trouble sorting out my video head. The Manfrotto QR clamp is physically part of the head so in my case I machined out the whole area to take a 50mm AS clamp. So all my tripods and heads work with everything converted to AS (except for the couple waiting for the adapter). I was looking at making an adapter plate from a Manfrotto plate to a AS clamp but decided to go with the machining instead. If you don't have a video head then everything was quite easy.
Been a bit of a mission but now happy that all is working. The AS fittings make macro-photography more stable.

I have a Manfrotto tripod that I like but it does not take Arca Swiss. I am considering getting a different tripod or at least changing heads.

I think I want to be able to use an L bracket. I am interested in feed back on L brackets and their use. I use a tripod quite a bit and seldom do vertical shots because of the hassle. It seems to be the way to go but it is an investment so I want to be sure.

I use both a full frame camera and also a D500. I see several choices for brackets for the FF - RRS, Kirk and others. As far as I can tell, RRS does not have a bracket for the D500 but I did find one Kirk model. Is there some reason not to use an L bracket on the D500? I was surprised RRS did not have one (unless I missed it). EDIT: RRS does have one. It is just currently out of stock.

I would appreciate any advice on these subjects.

Carol-since you have multiple camera models, I think I would be inclined to get a generic bracket that would work with most/all of your bodies. After using the bracket, and you decide that it's really a way to go(and I'm pretty sure you will), then decide which body would be used the most and get a quality bracket for that body. You'll still have the generic for use on the other cameras. When I'm in the Smokies, my RRS L bracket stays on one of my 7D2's. As for the tripod, I have a couple of Nest carbon fiber models. I'm leaving town next week and would be happy to lend you one to try out-drop me a PM.****edit: I also have a gimbal you can try as well.