If I read this correctly, you are asking:
1. Should you tell your SB you are having sex with other people (SO, casual hookups, multiple SB's, or pros)?
2. What is the "guidance" on BBFS?
Both of these are, well, slippery (no pun intended).
First, I always assume any and all of my SB's are fucking someone else. It's just not realistic to think otherwise - even if she tells you she only sees you. In her mind "only seeing you" may just mean you are the only SD she sees, so that won't include BF's (current, ex, and/or new) or a bar/rave/party hookup. But, in my experience, most SB's don't want to be cast into the "one of many ho's I fuck" mold by an SD. So what you tell her? Maybe nothing, especially if she never asks. If she does ask, you will need to guess how specific she wants you to be, as well as how specific you want to be. For me, I always refer to other SB's in the past tense and let her assume that I mean BEFORE I started fucking her. Even if I saw another SB (or pro) yesterday, that WAS in the past. Coloring the truth a bit? Yes. But I don't like to lie. Lies bite you in the ass eventually.
On the other hand, some SB's not only don't mind, they may get off it. If you frame it like she's the BEST, TOP, #1, blah, blah, blah, she may take it as a compliment and enjoy the competition for more of your cash, and so do everything she can to get a bigger share of your time/money. Or she may just be truly "polyamorous" and not care. Pay attention to how/if she asks, what she has told you about past partners that cheated and/or lied to her, and how much of her "trust" (or lack of trust) of you is based on her past bad experiences. There's a concept here we don't talk about much around trust: How much should you "punish" your new SB for a previous SB's bad actions? Well that goes both ways. if she's been burned in the past (by getting an STI or pregnant), she may be much less willing to tolerate "cheating" from you. This also applies to the BB topic coming up next.
Second: Going bare in the sugar bowl is a similar balance to going bare with a pro, although with a pro you absolutely KNOW she is fucking others. Mutual & frequent testing, and sharing results (I mean showing, not saying), plus some knowledge (or best guessing) about her concurrent partners are needed to decide if you want to trust her. And it's the same for her. I have missed out on several otherwise great POT's because they either would not agree to testing (and birth control) or even mentioning the topic was a hard stop for them. So you need to decide IF you really need to go bare, or just hoping it's a GWP (Gift With Purchase).
So how do you approach these? For #1, I would just stay away from the topic unless specifically asked. Then I'd ask her several questions about her experiences and motivations before I develop an answer strategy. For #2, you need to decide how important it is you first. Then if you think she's a bit hesitant, try doing all the pro-active stuff on your side 1st, like casually mentioning that you just got your (monthly/weekly/quarterly) test results and her they are. Then maybe ask her if she has been getting tested (if you haven't already done so. I always bring up testing before I make an offer.). Then take your lead from her reaction and questions. But if you are already in an arrangement, take it slow and don't push her to do something she never agreed to do when you started.
But all this is just my approach. Others may take a different POV...
Life is good
The Cat 
OK, there was one exception I remember. A 20-something Asian SB in DC straight up told me she used to be an escort. Without getting into what was different about her now (!), I told her I had seen escorts and it was a point of commonality.
My experience is most of the SBs I've met seem like they would react poorly to revealing a past or present with escorts. (Maybe I misread this?) Most of my SB experiences are with girls who apparently see SB-ing as totally different from escorting. Yes, that includes the ones whose profiles blare, "I am not an escort!" but who I am still able to take to bed on a first date for a PPM. (The thing that makes them not an escort is the clock is not running and they are less likely jaded.)
It seems like it should be possible to keep completely separate the matter of escorts, and BBFS.
