when i install ubuntu do i let ubuntu install it where it likes
Do you mean to let the Ubuntu installer make the installation partition selections? I would suggest you do custom or advanced installation as you will have more control. Either way, you just need to know before you begin the installation where your Mint and windows installations are, on which partitions so you do not overwrite either.
Grub2 should detect Mint and windows and put an entry in the boot menu for each. If it doesn't you should be able to run update-grub to add entries. Without more specific information on how many drives/partitions and where each OS is it is not possible to give more detailed suggestions.