Purchasing a mac, need help

Hello fellow mac lovers! I have been using the same black macbook for the last five years and i bought it used off a friend for 700 bucks. a great deal then, and I have absolutely had my moneys worth out of this thing. But it has already froze 3 times just while writing this much.... needless to say, it is time for a new computer. I am a college student who is a Marketing major, I require a computer that can perform video and photo editing but also that is lightweight enough for me to bring to class and work from regularly. I have access to imacs at school for larger projects but I literally live with my laptop by my side. I have four options: buy a refurbished macbook air 13" or macbook pro 15". or buy a new Macbook air 13" or macbook pro 13". I figure go big or go home, which is why i opted away from the 13".

there are 13" refurbished airs for $1200.
Refurbished MacBook Air 1.8GHz dual-core Intel Core i7
Originally released July 2011
13.3-inch (diagonal) high-resolution LED-backlit glossy widescreen display
4GB memory
256GB flash storage
Thunderbolt port with support for up to 2560-by-1600 resolution
FaceTime camera
Intel HD Graphics 3000

there are 15" refurbished pros for $1360:
Refurbished MacBook Pro 2.2GHz Quad-core Intel i7
Originally released October 2011
15.4-inch (diagonal) LED-backlit glossy widescreen display, 1440-by-900 resolution
4GB (2 x 2GB) of 1333MHz DDR3 SDRAM
500GB Serial ATA @ 5400 rpm
8x double-layer SuperDrive (DVD±R DL/DVD±RW/CD-RW)
Intel HD Graphics 3000 and AMD Radeon HD 6750M

NEW 13" Air for $1630:
2.0GHz Intel Dual-Core Core i7, Turbo Boost up to 3.2GHz
8GB 1600MHz DDR3L SDRAM
256GB Flash Storage

and NEW 13" pro upgraded Ram for $1400
2.9GHz dual-core Intel Core i7
Turbo Boost up to 3.6GHz
8GB 1600MHz memory
750GB 5400-rpm hard drive1
Intel HD Graphics 4000

So I assume that i7 is entirely necessary. and that I should upgrade the ram... but i am paying for this myself and using their payment plan so I am trying to keep the cost down... their interest is crazy!!!

BTW frozen 13 times so far... -_-

Ideally I would buy the refurb Air and upgrade the Ram third party style... if i can. I don't really know. so I need help. plus i worry about the Air not being able to handle my editing needs. as well as the possibility of bootcamping it.
the 13" seems like the best deal, but I really want the Air. maybe i should buy a ipad and a 13" idk. but this is getting expensive and my computer is now up to 15 freezes... so please please please help! again, looking for need first, but PRICE ABSOLUTELY MATTERS. cuz its all outta my pocket. thanks mom and dad :/

 

Thanks for responding so quick. It really is time for a new computer, as for my old one, it had a good run! But as for short run operations, i will look into it!

EDIT>> quick note I edited my first post, and realized that buying a NEW 15" is just not worth it, too much money for it to be upgraded to what i should need.

 

I looked up the swap used and page outs: 0 bytes... but the only thing I have been running the last week or two is chrome. so I have no idea if that is good or bad

 

Can you not 3rd part upgrade the Ram even on an older macbook Air? And yes it as absolutely come down to an Air 13" vs MBP 13" haha.

So I am looking at a refurb air that is $1200 with 4GB ram, an 1.8 Ghz i7, and 256 G SSD.

New air for $1630: with 8GB ram, a 2.0 Ghz i7, and 256 G SSD

New macbook pro for $1400: with 8GB ram, a 2.9 Ghz i7, and 750 GB HardDrive...

If I am getting the best deal possible i would think the refurb is the way to go, cuz 4GB ram =/= $400. but its also the older model.

but since I am a tech amateur, please help with these questions.
So i guess it comes down to three things. is the i7 processor THAT important/better than the i5.
Does 1.8-2.0-2.9 GHz make a large difference.
and could I live with 4GB Ram or is 8 needed?

because I could buy the i5 Air with 8GB Ram...

in the end, I just want a mobile computer that I can do my editing on. I always dreamed of the Air but maybe its not the right thing for me yet.