Yes, you can absolutely write
It isn't trustworthy. You should put one to show that you are legit.
Yes you can make two portfolio, but you should mention little bit of your secondary service in both the portfolio.
You can have a look here at on How to build a personal brand.
Niche down, Become expert in your niche, Network with top 1% in your niche, Build a strong personal brand.
Build personal brand, work with clients, posts results / testimonials / works realted.
Niche dowm, Become expert in your niche, Have a strong online presence.
You can make two portfolio, to reduce confusion for the clients, but mention little bit of your other service in both the portfolio.
Start by connecting with top people in your freelacning niche, provide value for free, Engage with your audience.
It is not compulsory, but it is very useful as it portrait you as a legit service provider.
Linkedin, Facebook, Twitter, Youtube, Atno.
No, it is nothing but building a strong online presence you can know more about how to build personal brand here.