Re: admin not working
If I understood you correctly and your SSL cert doesn't arrive until Monday - trying to set things up without it will break things.
Zen Cart code is smart - it knows what pages need to be SSL and when to switch, but you have to have the parts and pieces in the right places and in the right order. By setting both defines to your https address and having the Zen Cart files in the HTTPS_DOCS directory on your server - you will have both the Store and the Admin working only in SSL mode.
Do you want your Zen Cart to operate normally (switching when needed) or do you want everything under SSL?
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Be careful with unsolicited advice via email or PM - Make sure the person you are talking to is a reliable source.