Actually, brown widows are not that dangerous - http://spiders.ucr.edu/brownwidow.html. They are also not particularly aggressive.
Correct, I noted they were more poisonous than the female black widow, not more dangerous. And I agree. not as aggresssive however when you are bumping into them and pestering them as I was with the web & spider hitting the lens this would be good cause for them to be more aggressive as it would seem.
It is certainly possible to focus stack handheld at higher magnifications. I provided one example below. Look up the work of LordV. He does hand held focus stacks with a 10x objective. It's possible - you just need patience and practice.
Ahh, the infamous Lord V. Yes I know of him for quite some time. Been to his site and recall he is a biologist and lives in the UK. If hand holding works for you on focus stacking more power to you. No matter how you slice and dice it though, a tripod is going to be unequivocally more stable than a human holding all that gear. Everyone's body shakes to some extent. You have less likely of a chance on getting the camera in the same location in space (X,Y,Z coordinates) so unless the situation doesn't permit for a tripod, I'd rather avoid hand holding all that gear for the aforementioned reasons. In looking at both scenarios, accuracy would prevail on a tripod with a macro rail hands down. Again, I am not saying what you are doing is not possible, however these are my preferences and those are yours. I prefer to shoot with a tripod and rail when focus stacking if probable and the situation permits.
Live View is useful if you have a subject that is staying still for you and have your camera steady on a tripod. I do use it when focus stacking flowers, but for insects I find it completely impractical. If you pay attention to the eyes of your subject you can obtain focus with extremely fine accuracy. There is also a custom function on the MT-24EX to turn the lamps on with a tap of the shutter button. With a moving subject you really need to use your eyes for tracking.
Again, no hard fast rules here and this is why we have options. I use the view finder almost exclusively for all my shots however for my personal preferences I use Live View for Macro work/video and photo review. The 10x magnifier works great. Also, my eyes are not your eyes. If I had never used the VF then I'd say yeah I'll give a try but that is clearly not the case.
BTW, why did you have the MT-24EX heads on the gorilla arms? Was it to keep them from getting tangled in the web? Generally I leave the heads on the front of the lens and adjust them as necessary. The only time I move them off is when I need to adjust the angle of light due to a highly reflective subject (most often water drops). In this case I use Wimberley macro brackets. This is why you had to use so much power. In this case you're probably better off just using two 580EX or similar flashes because you are losing the close light that the MT-24EX provides.
You are right. I was getting a bit too much reflective glare on beetles and other reflective objects and in addition the ring that comes with the 24EX was sometimes causing bumping into objects unintentionally. I've read many complaining about this and the gorilla arms are a good alternative and less restrictive though the downside is possibly more light consumption. So your point is well taken, having the flash off that ring would cause the need for more light no doubt as the key light source is further away.