How to find the best potion to make: The basic idea is to add up how much you lose from making the potion, then divide that by how much exp you get.
Example: Strength potion, to make it you need a Clean Tarromin, a Limpwurt Root and a Vial of Water. The prices (as of today) are 211 for the Tarromin, 1,050 for the Limpwurt Root and 66 for the Vial of water. A total of 1,417gp. Now the potion itself is worth 1,076 (3 doses). So you lose 341 gp per potion you make, and you also earn 50 Herblore exp, so 341 divided by 50 is 6.82.
This means (as of today) you will spend 6.82gp for every 1 exp making strength potions.
It's up to you to find the best deal daily because prices change.
Also, for collecting your own vials, if you make more profit per hour collecting vials then you could using any other method, first off you've found a new way of making money, then it's worth it. I don't know how much money you can make per hour collecting vials at Ardougne, but I would assume you would be able to make more money doing something else, therefore it would be faster to use the best money making strategy you can and then buying the vials with your profit.
I hope you understood all of this and I hope it can help you with your herblore training.