Welcome to the Vulcan madness. Sorry about all the trouble you are having.
It might help if we knew the mileage on the bike and its overall condition.
How far did you ride the bike on the test ride and on the way home?
Did it have good power during the ride?
I suggest doing a compession test, then pulling all the plugs and doing a spark test too.
Was it stored inside, or does it have surface rust, etc?
Has it been sitting for a year or more without being ridden?
Here is a link to an online motorcycle repair course that may be of help to you.
Lots of topics to choose from as you need them.
I am not sure from your opening post what the current problem is.
Did the rebuilt starter not spin over at all, or just not have enough power to turn the engine over fast enough to start?
Is the new battery fully charged up?
Give us the answers to these questions and we may be able to give you more help.