New to Linux: Dual Boot Windows 7 SP1 and Ubuntu 14.04.3 LTS (GNOME) Questions/help

OK, so I'm wanting to dual boot Windows 7 and Ubuntu GNOME. I've
heard some really good things about GNOME and Ubuntu and wanted to see
what it is all about, however I would like to keep Windows 7 for
programs that will just not work with linux and am not interested in a
virtual machine/wine. This will be going on a Dell Inspiron 14z laptop,
with 500gb HDD (around 250gb of available space). I just wanted to
know if there are any steps I should be taking to make this go as
smoothly as possible as I am a complete noob with Linux. I've reviewed
the following documents:

http://heather.cs.ucdavis.edu/~matloff/Linux/LinuxInstall.pdf
http://www.dell.com/support/article/us/en/19/SLN151792/en
http://www.dell.com/support/article/us/en/19/SLN151841/en
http://www.dell.com/support/article/us/en/19/SLN151748/en

After reviewing this literature I have taken the following steps to prepare:
Back up all of my important files on external HDD
Create a system image on a external HDD

I've also used Canonical to review compatibility and believe that my system is compatible.

I would like some advice on how large I need to make my partitions along
with any tips or tricks would be greatly appreciated as I would like to
have a pleasant first Linux experience.

I've tried watching some tek syndicate videos, however those videos go into a
lot of depth and are really tailored to specific scenarios (the Surface
Pro 3 video made me cry) , some more documents or tutorials would be
appreciated if you could recommend some.

Thanks, look forward to your comments and input...

ok if you have backed up your nearly ready to go, test your back up! does it work? did you really check it??? i will wait XD

Ok right click on My Computer and choose manage->Disk managment
shrink your c: partition if your just testing 20gig is about minimum.

reboot with the cd in the drive and choose install Ubuntu. Wait a bit then on the disk partition screen there will be any an "install along side windows 7" option. then just next, next, username, next next hopefully that will do it.