Translation:That computer is expensive.
These structures are all available:
Number + measure word + noun: 一台电脑，五个人
Demonstrative adjectives 这/那/哪: measure word + noun: 那台电脑，哪本书 (Only for singular words. For plural form it should be 些, no matter what the measurement word for singular form is: 那些电脑，哪些书)
Not necessarily. It's there for grammar's sake and doesn't always have the meaning of "very."
Yes, “很” is very often used as a connecting word; you'd be able to tell by the speaker's expression whether they mean very or not. Sometimes I've heard it repeated when the speaker wants to say it's VERY something: e.g. “很贵很贵!” kind of like saying it's really, really expensive. Of course, you could also say “真的很贵!”
hen is also used to connect subject to adjective. Using 'to be' is just so unnatural.
I'm wondering the same thing, why 个 'ge' as a measure word instead of 台 tái for computers/machines?