I make my own unflavoured base with a target of around 16mg nic once the flavours are added. I only make about 30ml at a time, which lasts at least 3 weeks, and it means I can adjust nic levels and PG/VG ratios if I want next time round. In the early days, I played around a lot with ratios and settled on 50/50 base, but I've dropped from 18 to 16mg nic recently. I'm not sure I'd want a large bottle of fixed nicotine levels.
If you're looking to play with flavours, there's really not much more to it by adding your own PG/VG to your nic base.