Cly_Faker
Liking YTtalk
I agree that GIMP is a great choice, but I have another piece of advice about thumbnails. You're going to want some fonts that you can use commercially, and I've found 1001Fonts.com to be a great source. You can browse by tags, and there are a ton of free fonts that allow commercial use. You don't even need to click the font to see what the licensing options are (the green price tag icon means you're good to go).

