How many songs can be store in an IPod touch 64GB?

If you plan to just load up on music and do not load up on apps and leave about 4 GBs of free space for reliable iOS operation, and depending on the encoding quality, data compression or not, anywhere from, at least 4000 songs and, potentially, up to maybe 8,000 songs or so, approx.

My new, 6th gen iPod Touch, 64 GB storage (56 GBs of usable storage space) has my full music library on it with about 2000 songs that use 16 GBs of storage on my device

I use either AIFF or Apple Lossless formats at the best quality encoding settings.

I have about 23 GBs of free storage space left.

So, I would only be able to get up to another 2500 songs, or so, if I use another 20 GBs of free space for music, for an approx. total of 4500 songs.

Capacity

32GB or 64GB flash drive2

Holds up to 7,000 or 14,000 songs in 128-Kbps AAC format3

128 Kbps second is compressed. Also that is average some songs are longer and thus take more storage.