It strongly depends on how exactly you want to use a MIDI keyboard in combination with a C64. For instance you can try Triad MIDI Slave Manager and SID Wizard. If you just want to jam around a bit try Cynthcart. And there's even more software avaliable.
Maybe your question isn't formulated precise enough to be answered exactly.
software package to play and record music
only a DAW does this (if you mean: audio = "music"), not a C64 with MIDI and software, unless you mean the small data like in Cynthcart or MSSIAH, there you can save it to floppy or comparable devices (but MSSIAH doesn't need a Datel Cart).
the data could be huge, so maybe they are meant for recording in another way.
"save" = data, maybe patches, your songs as sid playable files ?
"record" = huge data, maybe audio ?
No problem, I think the basics of MIDI (the MIDI from 1983. There's a new MIDI 2.0 that comes this year but it's not a theme yet) are to know that it is
- control data without making any sound or audio data. Your keyboard (or a MIDI software, a hardware sequencer, controller devices etc.) sends it, the devices at the destination (for example synthesizers, Cynthcart & SID chip) receive it and play the AUDIO data
- due to the fact, that MIDI 1.0 doesn't "know", what the destination is or makes with the MIDI data, it's normal that the destination (or its parameters) has to be adjusted to make the sound(s) you want to hear from it. You play the keyboard and adjust, for example, the patches at Cynthcart
AUDIO:
You're right with the recording to audio recorders (I add soundcard with recording software), because even the 80s CD quality (16 bit with a sample rate of 44,1 kHz) needs approx 10 MB a minute, if in stereo
is for live performance
and more- with MIDI you can play it live or arrange everything with MIDI software. Even both (play MIDI, record MIDI in a software, edit the data, let the corrected results be played by the software again and the destination receives it). The old MIDI is simple but very versatile.
Slow fits to retro, slowing-down can be a quality nowadays 
Good luck with your start and Cynthcart !
Makes perfect sense, thanks. I have a bit too many toys (and real life work) so im slow at getting started, but eager to jump in. Cynthcart seems to have a lot of recent buzz, so I may start there.
I am having got a DATEL MIDI-Interface as well. Since MIDI was a standard, MIDI software from other companies very often supported the DATEL MIDI-Interface, too. I would suggest to have a look around C64 MIDI software in general.
Will definitely do that, thanks!
In case you are not successful, I'll be here.
Station 64 seems to be a great tool to play via midi with custom sounds: https://csdb.dk/release/?id=142049
I can only recommend putting a sequencer between input and output device (and having more output devices is more fun). My favorite sequencer that is easily available is the Alesis MMT-8, simple to use and great for building up own ideas. There are sequencers for the c64 as well, but they are harder to use.
