Nice one. It really is very easy. I use the E-Juice me up calculator and it hasn't put me wrong ever.
Custard recipes generally take at least 4 weeks to steep. Don't forget that. Butterscotch will probably be similar time frame.
I LOVE Red Astaire from T-Juice. The concentrate is only around £4 for 10ml (IIRC), and is good to vape pretty much as soon as you've shaken the bottle. It is best after a week mind you, but you can vape pretty much straight away if you want.
Minty The Toff is another great T-Juice flavour, and is my second favourite.
Good luck with your mixing adventures.
Thanks for the tips. I don't mind waiting for them to steep, I have plenty of pre-made to last a few months.