Need a policy for custom orders and I don't want to miss anything, what do you include?

[x-post from r/etsy] I have a lot of experience working with clients to create custom jewelry face-to-face, but I'm getting some requests for custom designs at my etsy shop. www.etsy.com/shop/kareszajewelry I would love to create jewelry with customers online, but I need some terms and conditions. Looking for advice because I want to be smart about this. Here's what I got so far and the questions I've had along the way:

When any customer shows interest in creating custom jewelry, I'll create a private listing with a name and whatever details I have. I read that many of you do this, I am wondering how you price the listing in this stage, before any quotes have been discussed? $0.00? Do some of you charge a design fee for the time brainstorming back and forth?

Design details are discussed, materials assessed, timeline established, design approved. During this process how do you track and communicate about the cost of the item? For example, a woman wants silver spacer beads, I show her my inventory of small beads then give her a quote with the cost of my beads. Then she says she wants them to be the same size as the rest of the beads, which means I have to order them, would you then change the quote to include cost of new materials and shipping? I keep as much in stock as possible, but if I have to order it, it costs me more money, making the piece more expensive, do customers get that? How do you tactfully explain an increase in their quote? Besides getting the materials, labor and processing time defined, are there any questions you guys are sure to ask to ensure your quote is accurate? I don't want to forget anything.

After the design is approved I am going to ask for money. I haven't decided if I will do two transactions or one. My custom pieces are usually between $100-$200, is that too much to ask for upfront? What do you think? And those of you who split it up, how do you go about that? Charge for materials first, labor later, or do you just cut the quote in half?

Finished the product, shipped and delivered. I figure no returns or exchanges for custom pieces as they cannot be resold. If a customer expresses some kind of dissatisfaction, do you offer to make revisions, talk with them and then try to offer a quote for the revisions? I worry about those custom orders that just never seem to end. How would you keep track of this? Create a new listing for the revisions?

Also if you guys have any disclaimers, terms and conditions, policies or guidelines I haven't considered, please let me know!

Thanks so much!