Only advantage of heat (gentle heat with warm water bath or the like) is to make the VG easier to mix. I mix high VG juice but don't find it particularly difficult to use or mix.
Good shake every day, leave lid of bottle on to allow the chemical process to do its job. Only open bottle to check near end of expected steep time.
Nic is nic and is not a "base" to just add flavours to, very important to know the difference between nic solution and a ready mixed base (base will be a mix of PG and VG and sometimes nic to which you simply add flavour).
A lot of questions on here recently, easy to see that there is confusion out there, so do be very careful unless you're using no nic.
Check, ask, double check, use two calculators and your own maths and ask again. Once you get it right you'll be fine but take care, don't overdose on nic.