I thought that I "must" interfile if I have two apps running at the same time.
That's not true, you can have multiple I-485's active at the same time, provided they're based on different petitions.
So is it ok if I file spouse without even informing the current applications processing center that I have another application at the same time? Would the USCIS/interviewer get aggravated if he found that I also have another application going on?
Take the same A-number you got from your existing I-485, and write that in your new I-485 paperwork wherever it asks for A-number. With that information, USCIS should make the connection between your old and new applications. At the marriage-based interview, tell the interviewer about the EB case (bring a copy of the EB I-485 receipt), if it's not clear that they are already aware of it. But you don't have to tell the employer until later (see below).
Is the process to self file for FB relatively easy provided I have all the necessary documentation?
Yes, unless you have some complicating factors like a criminal record or certain other immigration violations. But you must prepare for the interview.
Should I let all her name change documents (ssn,passport,id) to come in before I start?
That's not necessary. She can write her new name in the paperwork where it asks for her current legal name, and write her maiden name where it asks for maiden name or other names used. The marriage certificate will provide the connection between the old and new names, and she should bring the updated passport and ID/DL to the interview.
should i inform the company and lawyer once i actually get my greencard to withdraw the eb petition?
When your FB case is close to approval or has been approved, USCIS will cancel the EB I-485 and notify the lawyer. Better for you to tell the company and lawyer first instead of them getting the message by surprise from USCIS. But don't tell them too soon ... wait until right after the interview (or maybe right before the interview, if you need time off from work to attend the interview). Because if you tell the company too soon, that might lead them to get lazy with your EB case, cutting funding or not responding to RFEs etc. It is preferable for you to be approved in the employment-based category, since that directly gives you a 10-year GC whereas marriage-based would give you a 2-year conditional GC followed by another round of paperwork and fees 2 years later to extend it to a 10-year card. So avoid prematurely giving the company a reason to slow down or cancel your existing EB case.