Where im getting is that is not as simple as you think it is... And cubase has come a long way. Maybe you need to catch up with all its new features. A lot of [people gave up on their 20 grand mixers and dozens of thousands of pounds just to trade it for a more digital based one. I still keep my fully analog based studio with a 48 channel mixer and 24 multitrack recorder just cause i love the analog stuff, plus im a dub head, otherwise i can tell u i would have done the same. I also have 20 channels in and 20 out of cubase( as a back up thing and for more digital genres, as i also compose for many artists) and know cubbase quite well.. What you saying, even live is so easy, with it. If you knew how hard it is to match a loop to a live performance, you would give up now or at least understand what im saying.
Now if you wanna do it for proof of concept, you will definitely need more than just an arduino, i can tell u that now !! Hands down !!
Sit down, do a block diagram of all things and how they will work ( might be easier to understand), and you will start realizing what im saying !!
without a time signature, there is no loop. At least not a workable one, as would be all over the place.
Record something, or use a live band track, and try to make a loop out of it....and note the time and how hard will be to do so !! Then let us know