congratulations on getting your practice licence!
You need to apply for an agent givernment gateway account. From here you have access to all your tax services (Although for MTD VAT you need and Agent Services Account which is seperate).
There is no fee for setting this up. I'd suggest getting ytour agent access as soon as possibel as it can take a little time.
There is information on using the ICB crest on the website. You need to get written permission for each different use ie website, stationery etc.
As for marketting getting out and meeting people is the best way - current restrictions permitting of course!
Best of luck