I've been testing and experimenting for over a year now and am just about ready to start selling on Etsy. I think you've got the right idea to start with bases and expand from there. For me, it took a LOT of online research into ingredients and techniques and formulas to really feel like I knew what I was doing. I also tried every base I could get a sample of - the difference in quality is astounding. To start your inventory, I would recommend investing in a few really good quality body-safe fragrance oils and definitely research and select some good preservatives, since not all bases are pre-preserved. Once you are confident, you can move to customizing your bases with butters and oils for different characteristics, then finally start creating your own formulas. In my opinion, you definitely need to blend your fragrance oils in a 1:1 ratio with Polysorbate 20 before mixing into a base. I've never been able to get them them fully blended without it. You may also want to research thickeners, like Crothix, because some bases really thin out after adding fragrance oil and a touch of thickener will get them right back in shape. Here's a percentage conversion chart that I use every time I make something: http://www.wholesalesuppliesplus.com/PDFS/ConversionChart.pdf Good Luck!