I reinstalled CodeXL this morning briefly to answer your questions.
VS crashes on close (with a minidump and windows error reporting dialog) even with only a single instance running. I did not notice Visual Studio running slowly in the few minutes I had CodeXL installed today. I tried with just one solution and with all 8. It may take longer for the slowdown to build. When I was using it before, the slowdown was very significant.
7 have different solutions of one project each, one has a solution with all the other projects inside it. There are no warnings about files being locked by other instances of visual studio.
Windows 7 Home Premium Service Pack 1 64-bit.
AMD_CodeXL_Win_1.5.6571