Custom orders are great for business. I just opened my web store 2 months ago(I make quilted ornaments) and at first wasn't going to do customs. I recvd so many requests that i quickly added the option. I let customers select 1 of 2 ways I can do them: 1. they send me the fabrics to be used(I return any unused portion) or 2.they describe what they want and I purchase fabrics.this of course is more expensive. Since I use small amounts of fabric per order I only buy what I need and include cost in price. If they want something that I can only buy large amount of(and it is something I do not need/want) then I let them know and include cost in price and send remaining fabric to them.If it's something I can use in future I keep remnants and only chg for portion used in their order. This has so far worked for me and customers are happy with options. I hope I explained all that in a way that made sense
It is great that you are planning ahead & getting all details worked out. I spent 6 months planning" my site.
best of luck