if you go with the jd's, yes only 2 will be able to go there...

they have a good size bioload....but you can have other small fish with them like maybe 2 jd's and a pair of angels in the 55g? that way you have some bottom/middle dwellers(jd's) and some middle/top dwellers(angels)...but 6 jd's in a 55 would be way too much .. or you could go 2 jd's and your 2 salvani's in the 55g...only caution is if either of them are a pair, they primarily hang out in the same area of the tank and might have a war with eachother....
its a crazy hobby for sure and im glad you are back in there!! its a ton of fun and so much relaxation

would love to see some pics of your tank sometime if you care to share!