I think there isn't an inherent security issue with by using one account for both PR/Marketing and AdSense + analytics. However it would be best if you think about a long term solution here.
Whatever you business/organization may be, you might grow to the point where you will be doing or assigning separate duties to separate team/individuals. It's always best to plan ahead for when you'll (hopefully) be exercising proper security hygiene and separation of duty principles. https://en.wikipedia.org/wiki/Separation_of_duties
Some issues that you might have by making your main account public are:
- You may be more prone to phishing & spam
- You might experience brute-force attacks more often
NOTE: If you're using an old email for everything, it's always a good idea to check if your email/password has leaked due to a data breach in the following websites:
Stay safe :)