8.5 gallon is still way too small for a goldfish, but if you can't afford a bigger than, then I guess it will have to do.
First wash your new tank clean, same with filter.
Install the filter, make sure there is filter media in it. Fill the tank with water, use water conditioner in it. Make sure the filter is running.
You haven't told us what water conditioner you have.
What beneficial bacteria bottle are you speaking of? Tetra SafeStart is the only proven working live bacteria product for nitrogen cycle. If what you said is indeed Tetra SafeStart, then you may dump it all in at once into your tank water. Let it run for 24 hours before transfer your fish into it.
Old water has 0 value for transferring bacteria. You don't want it.
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