If you have 8.1 home you will get win 10 home not pro
In almost all situations your data should migrate seamlessly but as ususal if you value your data you should back it up
Win 10 FAQS http://www.microsoft.com/en-us/windows/windows-10-faq Win 10 features http://www.microsoft.com/en-us/windows/featuresWin 10 Specs http://www.microsoft.com/en-us/windows/windows-10-specifications
How to upgrade http://www.microsoft.com/en-us/windows/windows-10-upgrade