Depends on the size of your batch.
I still say do a 'make believe batch' to practice.
If you make 10 to 50ml at a time, individual ingredients can be added with a measuring instrument of the appropriate size.
(1 or 3ml syringe and a 10ml syringe). If you have a bottle of 500ml of 48mg/ml you will be opening it many times before it is used up.
For larger batches,
measuring 100 to 200ml of an ingredient like Vegetable Glycerin with a syringe would be a real pain.
Safety practices and personal protective gear not only keep the Nic off your skin, spilling it all over, but also help keep the individual ingredients from becoming contaminated or contaminating other things.
Get sloppy with DIY mixing and you waste, spill, contaminate, and make mistakes.