about the php version support, upload to host a php file with
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then view it with browser and check the version - that will also show you everything supported by that host.
tbh it's sounds a bit weird that a hosting provider will "force" you to physically change all .php to .php5 extension in order for it to work (or it seems to me i didn't understand you fully there).
i'm not really sure what's the quetion here as you talk both about php5 & htaxx.
normally, in order to create htaxx (static file) you can use your hosting admin panel (usually CPanel) to protect some dir with password, and it will take care of things for you.
if you want to make "dynamic db-driven htaxx" that is php-code-controlled, just use search, you can find few modifications posted here.