Bad news: 'You have a bad script loop and we can't do anything to help you find it. You'll have to find it and fix it yourself.'
I totally get this, they can't be responsible for a third party open source software install, there are too many variables and they don't want to be to blame if my entire content gets wiped out by accident because they have no idea what modifications I made. Still, SIGH. The error logs are not pointing definitively to the theme, the plugins or the core install. I have no idea how to identify a bad script in a WP site without comparing php code line by line with a site that is working fine. Fortunately I have the old WP site on the old domain, with about 80% of the same settings on it, including plugins and theme - working fine, I might add - so in theory I *could* actually sit down and go bleary looking at individual lines of code to find the bad script(s). But that seriously can't be the best/only way to solve this, can it?
Of course I have googled the errors, stopped in on the PHP, MySQL, WordPress and host support forums, and I have also spoken with web developers I know who build sites in WP on a daily basis. No one can help me without direct access to the code, which I am definitely not going to give anyone. (shooting myself in the foot and/or reasonably cautious? a little of both, probably ;-)) And even then it's a bit iffy - and hey, I don't have money to pay someone to help me, and who's going to review all that script code for free?
I am tempted to wipe the whole domain clean and install a fresh WP core and start over. I'd have my backup database of course, plus a complete text backup as well, so my content itself would be fine, I would just have to start from scratch again with the theme and the plugins. Something tells me this will be the fastest way to my goal, rather than diving into code I have no way of interpreting or identifying errors in. And it occurs to me this is a good time to learn about child themes, so I can make my modifications without having them written over every time the theme has an update to install. So it's not all a bad thing :-)
Looking forward to looking back on this as a learning experience ;-) Until then, time to roll up my sleeves and find a solution. Wish me luck!