I just wanted to ask, I am sure I read somewhere that you can use the current biometric data if you have them already, is this true?
It is not up to the applicant to decide. UKVI will identify those who qualify for biometric reuse and the applicant will be notified by email (presumably the solicitor if their email was used for the application).
The solicitor however, said it is useful to supply a few letters from family/friends to confirm they attended the wedding. I know this isn’t a requirement but wanted to get a second opinion, does anyone think this will confuse the application or is it really useful to have anyway?
Such letter are IRRELEVANT and carry no weight or influence on a spouse visa application. Anyone can write a letter and say anything, so they would be completely disregarded. Please, do NOT submit wholly unnecessary documents. HO knows what they want to see, which is why they ask for specific documents. Don't submit what you THINK is relevant, when it actually is not.
Also, any idea on when we may get a biometric appointment?
You will be notified by email.