IANAL but you don't need to relicense your program to GPL just to use a GPL library. You can relicense to something that is compatible with GPL, like say the MIT license. Then the combined form has to be distributed under GPL terms. But when you one day replace the library with something not under GPL, you can distribute combined forms of those under MIT.
That is correct. If you want to redistribute a mixture of different program components as one program, all the pieces have to have licenses that are compatible. If any of them are GPL, then the whole thing will be GPL; all the other licenses have to be cool with being part of a whole that carries a GPL umbrella license. MIT and BSD pieces are this way.
