If your new, like me, I would go with the straight option of "install alongside" during the install sequence. You can then choose how to "split" the HDD. 50/50 is ok. You can always use GParted to alter the partition size later when your confidence and experience increases. If your more confident use a custom partition set-up as mentioned above.
Use the standard grub loader if a newbie. You can always repair your mbr using the Win7 install disc if everything goes completely pair shaped. Or via a Live CD session
wayne128 explains how to do this hereviewtopic.php?f=46&t=123162
You can access your docs on your Win 7 install from Mint. If your going to need something, short term, in Win7... just copy and plop it into a win folder. Long term you could always use GParted at some piont to create a small (20 -30GB) ntfs partition usable by both to dump stuff ?
Just some newbie thoughts... although you may get some more elegant and informed answers