1) (yes they are nice, I have one on my 11" air and programs start quicker, also the os boot time is extremely fast) If you are going to get a SSD you'll want to get a 2nd HDD because 256gb isn't going to be enough storage.
2) If you can afford it the 27" is quite impressive and you get a ton of desktop space. Important when programing / designing and testing. The higher res system has a bigger graphics card because of the resolution it displays.
3) 1gb of texture memory is more than enough for awhile but if its cheap it can't hurt to get more.
4) Throw as much ram you can afford into the machine. If your savy enough to upgrade your own memory it will be loads cheaper (OWC is popular
http://www.macsales.com/).