You need to go to Apple's web site to confirm the models that will accept Yosemite for the online update, because they go by model numbers and even build dates. If it's anything over 4-5 years old, don't consider upgrading because it would be slow. Just to launch Mail and click on a message in the Inbox, and have it show its content in the email can take 32 seconds. It is almost like using a Windows emulator on a Mac and running Windows software. You're literally running two computers and software intended for a different platform in that situation, though my situation is not quite that bad, but it is irritating.
You will have to check with MS for compatibility. They can tell you if it is or not, because they are the one who wrote the code and coordinated with Apple (or didn't) regarding compatibility.
As far as I know, if you have an Android phone, you still can't hook up the phone to your computer for data transfer. You'd have to email everything from the phone to the computer and back, or dig out the data card after dismantling the Otter Box and put the card in a USB reader.
Safari has always been slow on my computer, and it's even worse in speed. You have to remember that later versions of the OS use more recent processors and has code to take advantage of the speed increases, which the older computer has to deal with at the expense of speed. I wish they would quit updating the OS and just focus on bug patching as well as security patching. I will definitely not be upgrading beyond Yosemity on this computer. It would be like running 80286 software on a 8088 machine with no turbo mode and on floppy drives only. No thanks. I wish I had the money to upgrade to the faster computers with the Retina displays, which literally looks like you are looking at a photograph-quality image of the world instead of a computer-generated image where you can see the pixels up close. Reading text with a Retina display is like reading a physical book. It would be well worth the upgrade if I had the money.