The Windows 10 free offer ends on the 29th of this month. If the flash drive has the capacity it should be fine. All your programs would be lost unless you upgraded to Windows 7 first then upgraded to Windows 10.
How smooth the upgrade to 7 would depend on if the computer is currently experienced problems which could be hardware or software related. Usually an OS upgrade on a computer experiences problems does not resolve the problems.
Windows 7 has been having the same issues regarding updates and there are many threads on the BC forum.
Depending on what the computer is used for and if there are any mission critical programs needed you may you may find a linux distro such as Mint would serve the purpose. Most Windows programs have a linux alternative. The distro would depend on the CPU and how much RAM you have. For instance Mint Cinnamon would run well on a good CPU with 2GB of RAM. Mint is the best distro for moving from Windows but I found Ubuntu to my liking.
Once set up your chances of getting malware are slim and none. If you have any further questions please post them in the BC's linux forum. Thanks.
I would recommend a minimum of 1GB or RAM vs what the video stated.