Its very close to impossible to accurately tell how many songs a device will hold. Because that comes down to the the file size of the songs and that can change drastically depending on the quality of the song, the length of the song, the compression of the file etc...
You can have a song that is 3MB, and a song that is 8 or 10MB.
Your best bet is to know how much space your 5000 songs are taking up in your iPod. if they take less than 35% of the 160GB Then you'll know if they will fit in a 64GB iPad.
But only you can know that. nobody else can possibly tell you whether they will fit or not, because nobody else knows how much space they take up.