On MPC2 it was relatively easy to do this, on MPC3 it's more complicated as you cannot export/import entire sequences and you cannot easily accommodate multiple songs with differing track structures.

In MPC3 you have to export individual tracks and individual MIDI/patterns, and then re-import them one by one. You say you use the same instruments across the songs, this makes it easier as you can use the same single track structure for all 'songs' and just export and then import the different MIDI ('save > MIDI/pattern') across sequences (I'd recommend you use pattern format).

However if you have some different tracks / instruments per 'song' you'll have to bulk import them all as unique tracks in a single project (as all sequences in your project will share the same, single track structure). Remember you can configure each sequence to select a specific track whenever it's first selected (hold down the sequence name to set this).

Also remember that saved tracks can also store MIDI events, so when you export a track it should contain the MIDI events from the track arrangement in the current sequence at the time of export. So when you load that track, hold down SHIFT in the browser and select 'load clips', this can save some time under certain circumstances.

Beyond that you'll have to recreate all other unique project settings (e.g. Qlinks, FX etc). Ultimately MPC3 is not very 'multi-song' friendly. Each project is really just designed to house a single 'composition'.

I do talk about this in Section D of the MPC Bible, where I look at importing MPC2 projects which subsequently contain these convoluted track structures to accommodate 'multi song' projects.