welcome to the world of 3D printer!

You will not be restricted to the materials the the seller produce/ sell if the 3D printer you will buy can support 3rd party materials. Most 3D printer can be allowed to use the 3rd party materials now. There are many models printers on sales. You need to contact the sales men and let them confirm if the 3rd party materials can be used on the printer you are going to buy. Try to select those printers that can allow you to use other materials as this will bring you more convenience and low cost.

For printers that are capable doing the metal and regular plastic materials, you need to search them on Google. This is the unique demand from your site. For most printers in the market, they are capable on doing the regular plastic materials and resins. For the metal printing, I am sorry that I have less knowledge on it. Maybe the printers specially designed for industry use can help you.

For the last question you threw out, I have no idea for it. Hope someone here can help.

Finally, hope you can get the printer that is fulfill your demand.