Do you stock inventory or buy it as you get an order?

Do not stock - buy as needed. You can buy grommeted samples from distributors at a discounted price for display.

If you are refurring to supplies in addition to needles you'll want bobbins, backing (medium cutaway, tearaway and hat; solvy and stickie backing if you have fast frames) and thread (purchase a range of basic colors). Don't buy too much of anything until you're sure you like it but then buy enough so you don't waste a lot of money on shipping and handling costs. Save shipping cost by taking advantage of free shipping deals and using a vendor that is close to you. Be aware of handling costs for small orders.

If you will be ordering from a broad range apparel vendor then order when you need items but try to take advantage of free shipping deals by meeting minimums. Take advantage of sales if you know you'll sell the item.

I think a lot of beginners buy too much speciality stuff they don't really need but you do need some supplies or else you'll waste too much money in shipping and handling. My mistake was I should have ordered an initial supply of thread instead of starting with just the 15 cones that came with my first machine. I wasted a lot of money buying spools when needed them rather than investing in some cones in a range of colors.