Ask your hosting company if they provide a sanitization/”unhacking” service. You’ll definitely need it – simply deleting the fake admin accounts is just another hack waiting to happen
Definitely reach out to your host – they will have access to “deeper” PHP error logs which will shed some light on this
WordPress in on itself is not slow – it’s either your host or an unoptimized site. Go to https://tools.pingdom.com/ and run a test – it may give some insight as to what’s going on
What I’d advise is “if it’s not broken – don’t fix it”. It might just have been a hiccup related to WordPress running out of PHP memory but getting around it in the end. Unless you’re actively seeing that error somewhere on the site, all seems fine from your description.
