that's awesome....that's gonna give you a lot more room to work with
personally, I'd move the 2 convicts into the 30 gallon and the jewel into the 55 as well as the bichir. you're going to really have to watch the 55 though because once the jag hits maturity it will wreak havoc in that tank. if you can't get the 125 in time you might need to get rid of the jag until you do get the 125 and then get a new jag.
the flowerhorn is most likely going to have to go.
as for the jag and 2 dats in a 125...yes they all do get rather large but the dats are particularly slow growers and if you can get silver dat(s), according to the thread in the dat forum they only grow to 12". the biggest question is whether or not the jag will get along with them and not kill them. jags are incredibly territorial.