Hello Dalton, first of all thanks for the big kind words haha, I think you've made my day! :)
Doing these models it's just a hobby I enjoy and I'm glad whenever I see people using my assets.
There are no stupid questions so feel free to ask away anytime.
To address your questions, yes you are able to use them anywhere, you can definitely modify them as you please, my only request is to not 'directly' just resell the assets ( that is rare anyway)
As for the second question, welcome to the Blender community, in order to make the low-resolution textures(64x64,128x128,256x256) textures not look blurry, you can change the image filtering from linear to closest( In Blender ) , and if you're using Unity by any chance it is called Point filtering if I am not mistaken.Here's an image (*in Blender) :
I hope this helps.