If you rip to WAV/CUE, then you can create a backup CD with no loss of quality, deconstruct it into tracks or encode down into whatever format you chose, but with no compression, that would probably be impractical... over 100GB for 300 discs, assuming they average half full - but if you can spare a whole hard drive for tha collection, making high quality masters means never having to repeat a rip.
Using a lossless encoder such as FLAC or APE can also serve as your "gold standard" rip, saving up to 50% of the capacity.
Using any lossy encoder, treanscoding to other encoders or compression levels compounds the losses and artefacts of the first encode.
MP3 is the most common format, but these days, one of the least space-efficient. If your target platforms support AAC (preferably HE-AAC / AAC+), then that will do higher quality , or a lower bitrate and capacity for similar quality.
192k MP3 is a reasonable compromise of space versus quality, though a VBR mode averaging around the same would be better quality, but some things don't like VBR, giving minor issues like inaccurate track time indication, or problems playing at all if seriously incompatible with VBR.