ok, you've got me confused a little, lol. you want to move the oscar to the 75 gallon and plant this tank? not going to work - oscars will uproot plants like you wouldn't believe!
bristlenose pleco IMO will end up getting harassed or possibly eaten by the oscar - oscars average 12 inches and bn plecos usually don't get bigger than 4 inches. plus, the spines on the pleco's 'cheeks' can get stuck in the oscar's mouth/throat and that could potentially end up being one dead oscar and one dead pleco.
for a 75 i'd say just house the oscar by itself. if it looks 'bored' being solitary then give it things to play with. a golf ball will sink, and the oscar could push it around its tank. floating toys are great too, since they tend to get caught in the filter flow and the oscar will chase it all over - mine does this with a plastic nerf ball. just be sure that anything you put in the tank isn't small enough for the O to get in his mouth.