Hello!
Ready to start and do a quick solution.
I had checked your screenshot and came to know that there are 2 issues.
1. Upload product image issue: Need to check the permissions of files
2. You got 503: It'a server-side issue
Myself Vivek and I have experience with Magento 1.4, 1.5, 1.6, 1.9, 2, 2.0, 2.2.x and recently i am working on latest version 2.3.4
Please share your existing website details.
Thanks,
Vivek