You're free to use this assets for your game. No worries. It's not mandatory to add credit, but sure is appreciated.
Thank you
Working solo is great considering the fact that you dont have any restriction, whether it comes to ideas or any decisions. But the fact that you have to do all the work is the most tiring part.
If you are confident, then go ahead give it a try. And also i would definitely suggest fixing a deadline for tasks so that you dont overspend more time on one particular task.
Cheers!