You can get a copy of Max (freeware for Mac) here, and do bulk conversion of your AIFF files to FLAC, or most other formats that are PC-friendly. Max is also (arguably) a better ripping software than iTunes. It uses CD Paranoia for error correction, which is much more vigorous that iTunes in that respect. In some instances I've had audibly better rips from Max than from iTunes. Good luck with your transition. I'd agree with Albert about backing up, which should be routine for everyone regardless of their circumstances. Always a good idea to have a backup off site too if possible.
Apple to Windows...Questions
Currently running a 24" iMac bought new in 2008 and I've recorded a ton of LPs to .aiff files via Audacity which now reside in iTunes. Due to financial setbacks/major life changes I doubt very much that this computer system will be replaced with another Mac when it eventually fails. How seamlessly can I expect the transfer and utilization of these music files to be going to, say, a $600 (new) Windows machine? Currently I'm using a fairly basic wireless setup for music consisting of computer>Airport Extreme>Airport Express>stereo receiver/speakers in which iTunes is controlled by the "Remote" app on my cell phone. The info I've encountered via Google search thus far hasn't been fully explanatory...Any input/advice here would be welcome.