Hosts' properties are rated separately, so that's not a issue as far as a lower rating for one property bringing down the rating for the other property. And it will be good for you to have a bunch of good reviews for the other property visible to guests, so they can see you are experienced hosts with happy guests.
And you actually can't list another property under another profile if that profile uses the same info- name, phone numbers, ID, bank account, etc. One host, one profile.
However, when it comes to your metrics for Basic requirements and Superhost, the ratings will be averaged together. I'm not sure why you're concerned about that, though- is there some reason you think you might get lower ratings for the new property when you are obviously good hosts with guests who give you 5*s?
I would think that psychologically it might be a bonus for a new property's reviews that guests can see past reviews on your profile. People tend to be copycats when it comes to reviews- if they see a bunch of glowing reviews, they're less likely to want to be seen as a complainer. Whereas if it's a cleanskin listing, they might view it as a empty slate to get up on their soapbox and fill with criticism.
@Kristie-and-Joanna0