To say an iPad is a computer is like saying a car engine is controlled by computer. It is not really like a typical tower or notebook computer. It has no USB and no Firewire, so the only way to send or receive files is wirelessly or by buying the Apple Camera Connection Kit -- but it is limited to photo and video files. The processor is quite dismal compared with any typical notebook computer (only 1 GHz). RAM is only 512 MB. It uses a different operating system, not OS X, so you cannot use typical OS X apps on it.
Air is lighter than MacBook Pro, because....
-- No optical drive.
-- No Firewire 800 port.
-- No ethernet port.
-- The 13" Air has SD card slot; 11" Air has no slot (17" Pro has ExpressCard/34 slot; smaller Pros have SDXC card slot.
-- The 11" model has a smaller screen.
-- Data storage is by "flash-on-board" like an iPad (no removable HDD of any sort).
Other differences...
-- Less powerful processor
* * Air has 1.6 / 1.7 GHz dual-core Intel Core i5 with 3 MB L3 cache
* * Pro has 2.2GHz or 2.4GHz quad-core Intel Core i7 processor with 6MB shared L3 cache or optional 2.5 GHz quad-core Intel Core i7 processor with 8MB shared L3 cache.
-- Lower graphics power in the 11" Air (256MB compared with 384MB).
-- Lower maximum RAM (Air is "on-board" RAM that cannot be changed or upgraded; 11" Air is 2 or 4 GB; 13" is 4 GB; Pro is max 8 GB).
If you choose the 15" Pro, the specs jump up a whole league higher, especially for graphics. Serious game playing (is that an oxymoron?) and serious HD video rendering start with the 15" Pro models.
Apple is focused on the customer appeal. For Air, it is light, light, light. For Pro it is power, power, power.
MacMini -- out of time typing the War and Peace of computer knowledge for you. See the link below.
You need to stop adding to your list. Make separate questions about each topic. Don't try to cram six questions into one. That makes it mighty convenient for you, but extremely annoying for everyone else, just like certain biological releases in an elevator. We can't offer one answer for 10 points that explains every detail about every product made by Apple. You can read.