Depends on what Linux distro you're installing. I use Mint. You should at least have / and swap, but Linux offers a lot of flexibility with this. I create the swap space first, then a partition for / and for /home and that's all (typically 4gb, 32gb and 32gb, but that's just my preferences.
Probably best to post on the Open Source forum for advice on recommendations for Linux.
The boot manager is that provided by your motherboard BIOS. Most BIOSs will let you select your boot priority or boot order, so if you don't press F11/F12 it will boot from the selected drive first. When you want to change OS you restart your PC, press F11 or F12 and select the drive you want to boot from; Since you have each OS on a dedicated drive the boot mangers for each of the OSs are on their respective drives.