I'm very new to mixing myself and,when I first made up my mind, I sourced all of my ingredients and equipment from a variety of suppliers. If you are lucky enough, during your searching, to find everything that you need at the right price, via one vendor, then go for it but there are often offers and discounts around if you hunt them out, so don't burn your bridges.
There is not a great deal that you need, nicotine base,dilluent (VG/PG and/or both), flavouring, and calibrated syringes. And of course, some 'empties' to store you juices in.
All the other 'magic ingredients' like sweeteners, bitter-ers, ets, you can add to your cupboard, as and when you feel adventurous to use them.
I found it very easy by starting super simple, with single flavour,50ml batches using concentrates that are good at 20%, this made it childs play, with nic base at the correct dosage the only thing that I had to measure, a bottle of flavour (10ml) and top up with vg/pg.
Good luck with your new venture.
ps, I've been vaping for nigh on three years, and it's only during the last couple of months, from diy mixing, that I've actually found that my vaping is costing me pennies, rather than pounds.