Do you know what size the tank is that you're getting from the neighbor? I would just wait till you get the new tank set up to get anymore fish. Moving them is very stressful for you and the fish, and plecos can be tough to catch... After you get the new tank up and running I would then save that 10g tank for a quarantine tank, then you won't have to worry about it introducing disease. And I would also avoid a common pleco, uless the tank you are getting is 125+ gallons. They can get almost 2 ft.