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Hi Stephen,
Don't know if I can answer all your questions but here's what I would suggest:
Get a copy of The Dobsonian Telescope by David Kriege and Richard Berry. It explains the design principles you need to understand. The book takes you through how to build an Obsession style scope. This may not be what you ultimately want but the sections on building materials, how to make an effective truss, how to build connectors, how to align the optics etc are all relevant no matter what you decide to do.
Write some goals for your scope design, you mention portability and visual observation. Think about what you really want from the scope - one person set up? no tools? What size car do you have, when and where you will use it. Then look at the sites on the net and see if there are any designs that meet your objectives. Mel Bartels site and Albert Highe's are a good start for ideas.
A 14 to 16 inch portable scope is certainly possible I have my doubts as to it being as easy to set up as an 8 inch dob. I have a 12 inch home made goto dob. It is easy to transport although it takes up most of my old commodore wagon's luggage space. I have worked out that a 14 would take about the same space because I overbuilt the 12. A 16 would be more of a challenge (but still doable). If you can buy a thinner mirror this keeps the weight down and makes everything easier.
Cost is hard to guess at. It depends on the materials you use and the design you choose. I like Mel Bartels ultra light approach. He takes a minimalist design approach which helps minimise cost (small mirror box, longer trusses, single ring secondary cage). Have a look at his Tri-dob to see what I mean. Your biggest costs though are the mirror, eyepieces and focuser. The other costs are minimal by comparison.
If you have a friend who can cut the parts it makes the project much easier. Most people make their own plans. I am not aware of any available on the net but there may be. There are free design programs you can use so you can draw the plans and give them to your friend. I use eMachineShop that was suggested to me on this forum. It is easy to learn.
Hope that helps,
Rod.
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