1. Just about any 50 pin HD can be made to work with the right software (Silverlining is a good bet) but this is not needed if the drive has Apple Roms (i.e., iif it has an Apple logo on it). If it is Apple-branded, then it should work straightforwardly with what you've got and allow an install with any of Systems 7.1 - 7.6.1 (base 7.5 is a good bet for the IIvx; 7.1 would be even better, but oddly enough, 7.5 will install more readily).
Just be very, very sure that you have the scsi ID and termination on the hard drive and the cd-rom drive set properly, as failure to do this will universally (i.e., in every attempt even to boot the machine) cause all sorts of problems. This is imperative - and has been the source of much confusion over the years, even among seasoned veterans. Best do some googling if this is unfamiliar ground.
2. A bad hard drive would not in and of itself cause your floppy to be ejected. That is more likely to be the software itself, the diskette or the floppy drive. In this context, it occurs to me to ask if it is definitely a retail 7.5 disk tools diskette that we are talking about. Not disk tools for 7.6.1 for ppc rather than 68k, or a version of 7.5 that was sold with something like a Powerpc 7500? That would cause your symptoms there: the installers were not all universal. Detail is where the devil is, to paraphrase the proverb, so give us more detail. Where did you get the cd you are talking about?
3. If all is well so far, describe exactly what happens when you try to boot with the floppy (does it chime, do you get anything on screen etc.).
4. Do the same for when you try to boot from the hard drive.
5. Have you re-seated/ cleaned with a pencil eraser contacts on the ram (and vram) chips?
