On the Windows 10 Insider Preview ISO download page, there are five options, Insider Preview, Insider Preview for Enterprise, Education and Chinese Single Language. Since I am currently on Win 10 Pro, do I choose the first option?
You can not legally use the same license to dual boot.
1 license = 1 installed OS.
Program Agreement - Windows Insider Program
The license for the released version of Windows allows for only 1 install of Windows - but the insider copy of Windows would be subject to it's own license.4. Software
4.1 Microsoft may provide you with software (including any fonts, icons, images, or sound files included with the software, and also including updates, supplements, and upgrades) through or as a part of the Program Services (collectively “Software”). Software includes Windows apps which are apps developed by Microsoft that provide functionality such as mail, calendar, contacts, and news that are included with and are a part of Windows. You may install and test any number of copies of the Software on your devices as detailed in section 4 until the Software’s expiration date. Termination of use or access to the Program Services, or the termination of this Agreement, terminates your right to possess or use any such Software. Upon termination, follow the termination instructions in section 10.
Also, as far as I know activation (digital entitlement) is tied to the device, not your Microsoft ID. Syncing shouldn't be an issue except that it will auto change things on you. You can pick and chose what's synced though.
Before you install Windows Insider Preview
For the latest system requirements, check out the Windows 10 Specifications page.
To be eligible for the Windows 10 Upgrade Offer, you must be using a qualified, genuine Windows 7 or Windows 8.1 device. This can include a device you already own. Some hardware/software requirements apply and feature availability may vary by device and market. Devices must be connected to the Internet and have Windows Update enabled. Windows 7 SP1 and Windows 8.1 Update required. Windows 10 is automatically updated. Additional requirements may apply over time for updates. For details, see How to upgrade to Windows 10.