Every model on this site is a downloadable 3D model you print out onto paper and build yourself. Kinda like a plastic model that you don't have to leave home to buy, or paint. Nothing gets mailed out.
No. Every model is a downloadable digital model that you print out yourself, then cut out and build yourself. If you don't have a printer, you can go to an office store to print out the models.
No. My printer isn't very good, and ink for it is expensive. Also, my talents lean towards designing models, not building them (you would be very disappointed). If you go to papermodelers.com and ask nicely, I'm sure one of the expert model builders who are members there will be willing to work with you.
If a model isn't on the site, I don't have it. That doesn't mean I won't have it, I just don't have it right now. Sometimes, I've never even heard of the plane ( I learn about new planes every day), so I haven't had a chance to model it. If you really want a model, you can commission it.
All of my models are designed for 110lb cardstock (also called index or cover). 67lb cardstock will work as well. Here's a great chart to explain the different paper types and weights.