When you want a swelling wall of feedback, you want to have as much gain (signal boost, not necessarily distortion) after your pickups as possible, but:
a) You don't want to rip up speakers, like you said.
b) You want to be able to switch it off for the times you don't want crazy feedback, hiss, and other problems.
For the gain, pretty much any signal-boosting pedal will do--distortion, OD, an EQ with boost, most compressors, etc. Distortion also causes compression, BTW, and that's why so many guitarists go that route. So the gain is easy, a $40 Danelectro pedal will do the job brilliantly.
Keeping the speakers from ripping up is the tough one, and yes I do think a hard limiter is what you need. The reason is that again you are trying to make the pickups as sensitive as possible by boosting the gain, to draw in and amplify the feedback, but you don't want an equivalent huge increase in the levels actually going to your speakers. Be aware that a lot of the bands that use insane walls of feedback are used to blowing and replacing speakers as a normal "cost of doing business", like buying strings. The problem is that good limiters are not common and not cheap. Also rack ones can't be disengaged easily when you transition from feedback to regular playing.
So the very best approach is to absolutely flatline your signal with one pedal. The whole point will be to totally smash your dynamics--that's why you want to be able to switch it off easily, i.e. pedal not rack. This should either be an extreme high-gain distortion, or a comp/limiter with an infinity:1 ratio available, set with an extremely low threshold.
This will not guarantee your speakers will be safe, but it's the best option available, unless you want to get into some seriously expensive gear.
A noise gate is not the tool you want, because what it does is shuts your signal off when the levels drop below a certain level--so they are usually used to prevent feedback.
