You wouldn’t need a ‘Z’ visa if you’re not getting paid – it’s considered ‘voluntary’ work and you can do that on a tourist visa. The problem with tourist visas is you only get 30 days, (no matter what you apply for), but you can extend them for twice x 30 days each, (Public Security Bureau), giving you a total of 90 days.
Almost certainly a declaration will flag up an inquiry and will in nearly all cases be refused. It’s not what or how long ago, its criminal convictions they’re asking for. If you have one you should declare it, if you do you’re probably so naïve and unworldly wise that you really shouldn’t consider travelling abroad. Read between the lines on this one Steven.
With all due respect