The first is free-hand, which is to say that you record piano and vocals at the same time and even if they’re off tempo the two are synced together. It will sound more free and raw, but you’ll have a hard time syncing rhythmic elements and timed processing such as delay and reverb in a consistent manner. The second way is to record on grid, whereby you’ll record to a click-track to steady your tempo. In this case, it’s best to record one track at a time, but that doesn’t mean you can’t sing to yourself while you record your keyboard takes.
The first option for writing hip-hop bass lines is to utilize the low to low-mid range. The most obvious choice for working in this frequency range is to turn to the electric bass guitar. These lines are loud and powerful but have a surprising amount of nuance and flexibility. An excellent electric bassist can bring a track to life, so it’s always worth considering recording a live bassist. They can create a lot of humanity in simple, unobtrusive parts, and add depth to otherwise dry, electronic-sounding beats.