Well, from my perspective in a room full of men told they can gangbang me my concerns would be...
Physical safety - I have no way to control anything that happens to me even if limits have been discussed (and, admittedly, this is part of the turn on also!!!)
STDs
Getting "outted" on video or by a participant - I would have to somehow have control of whatever video gets taken
Thats just the basics - Bottom line is there would have to be some serious adult supervision going on somehow...
Physical Safety — This is usually assuaged in the vetting process. It's best to find men you can trust will respect your boundaries and discuss any kinks you have before hand. This includes CNC (consensual nonconsensual) which can be very tricky and requires a HIGH degree of trust and I would not recommend with people you don't know very well.
STDs — you are well within your rights to request recent STI panels from all participants, especially if you want bareback.
Getting "outted" on video or by a participant — You're not required to take any video or pictures and if you do I wouldn't recommend letting anyone other than your spouse/guardian do so. If you're worried about getting recognized and having a guy spread rumors about you, that's always a risk in this lifestyle and I would again urge you to take vetting extremely seriously. It's the most tedious and mind numbing part of all this but may be the most important.
As far as adult supervision, your profile says couple so I'm going to assume you have a husband. It's his job to make sure your safe. If you require condoms, it's his job to make sure all the guys put one on and keep them on. It's his job to watch you and gauge your mood to make sure you are comfortable and to stop things immediately if things get out of control. I wouldn't advise doing a solo gangbang as lady, you need at least one person you trust there looking out for you and preferably someone not playing.
I've done probably several dozen gangbangs at this point and 85% of them have gone off without a hitch and everyone involved had a wonderful time. Of the 15% that didn't, 13-14% was because dudes that said they would show up just didn't. I can't tell you how many times I was the only one of what was supposed to be a handful of guys show up to a gangbang. The going rule seems to be invite 20 guys and hope 5 show up and prepare to be disappointed. The remaining 1-2% are things like one time everyone showed up and we started and for some reason she just wasn't in the mood and stopped things after like 3 minutes. Us guys were a bit disappointed but everyone left without a fuss and there was no issue. I have a few stories similar to that, but what I don't have are horror stories. The more you do this sort of thing, the more you can start to separate the assholes from the good people and the dreamers from the serious. The better you get at identifying red flags, the easier and safer things get. This could just be a fantasy for you, which is totally fine but if you want it to be a reality it is totally possible and there are all sorts of ways to make things easier on yourself. Let me know if you want to chat about them.
P.S. if you want a party with 20 guys who can preform in a group setting that is going to be extremely difficult to pull off, ESPECIALLY if everyone doesn't already know each other. First off, from the guy's perspective, that kind of ratio is not fun and can get awkward real fast. If all 3 of your holes are open and you have two hands you can at max keep 5 or 6 guys even semi-involved at once with the rest of them just standing around watching. Most fellas don't want to just stand around a bunch of other fellas naked with their dicks in their hands. Porn stars would find it difficult to keep it up in that situation and most guys are not pros. Once you lose the horny, erection producing headspace it's hard to get it back; you're setting up guys to fail here. Having something (the pool or ocean idea works there but finding guys is still a challenge) or someone else to do would help; trying to set something up at a large swinger event like Splash Mocha would be my advice. Or you could stagger start times of the guys and have it be more of a train that a gangbang, or you could try your luck at a local adult theater. I have heard of this type of thing happening (I was involved in a 15:1 gangbang once) but it's really rare for I think mostly logistical reasons.