Honestly,
none of these questions are really able to be answered by anyone but
you.
We can't tell you whether you'd prefer an upright or a cocktail. Or whether you truly have room for either.
We can't tell you how many controls you need. Who'll play it? Just you? 2 players at once? 4? Do you HAVE to be able to play some of the great trackball or spinner games (Missle Command, Centipede, Marble Madness, Tempest, Arkanoid, etc)? Are you really wanting to play the more recent fighters?
We can't tell you how big your monitor should be. What's "big enough" to you? What size & type of cabinet are you building? (15" wouldn't be big enough in anything other than a bartop for me, but that's just
my opinion.)
These are all things that you (and
only you) can decide. It's YOUR cabinet, not ours. It's YOU building it, not us.
Many folks here will be more than happy to give suggestions (which may turn out to be more than useless, depending on
your specific needs/wants) but that's all that can really be done for you at this point.
What you
need to do is spend a
lot more time reading these forums and checking out the examples link on the main
www.arcadecontrols.com page. Take notes. Save pictures and links to the cabinets that you like. See what others have done and how they've solved the same problems you have. Learn from others' innovations
and mistakes. Read the Newbie FAQ. Buy the book that's advertised all over these pages if you can't cull what you need from these pages.
And
then decide what exactly you need/want out of cabinet. Come back with specific questions then, and you're gonna get help which will actually be of much more use to you.
Here's a few basic comments just so no one claims I'm not helpful:
Sizewise, an upright will make more effecient use of space (unless your cocktail cab will also do double duty as a coffee table). Remember that you've really gotta have access to both ends if you want to play 2P games on a cocktail.
Controls are entirely dependant on what
you want to play. A 2 stick w/2 buttons each layout will play the huge majority of games in MAME acceptably. 4 buttons or 6 buttons each will add in the majority of the rest. As I mentioned above though, some of the most popular games require a trackball or spinner.