Welcome Pekka!
R Record enable
[*] Record
--------intense artistic expression--------
Spacebar Start/Stop
Delete Delete Selected
Shift B To previous marker
…over and over… 
Joking aside, it really depends what tasks you perform more often. Different people have different needs. Also, excuse the bad taste, but here is a thread that contains all the available keycommands for Cubase 11. (I haven’t found the occassion to update it for Cubase 12 yet, sorry.)
Just read through it with a huge cup of tea if you’re feeling bored, I’ve made some comments about which commands I find very useful. (my own subjective opinion of course)