I think you can have up to 25,000 songs on your iTunes Match account.
And yes it does not use any storage of your iCloud account
25,000 is a limit for uploaded and matched songs. iTunes purchased songs don't count so if you buy your music from iTunes there is NO limit.
So if you have 24,000 songs you ripped from your CD's and bought 30,000 songs from iTunes you would be fine with 54,000 songs in Match account.