Ah yes, another lesson learned. It only takes one time to swear 'never again'. I had years of skating free, then a few years ago had a close call S of Whitney with wet/cold, possible hypo if I didn't get out. Luckily, I basically sprinted 5 miles back to my car.
Anyway, the lessons learned are as you state:
(a) Get some MSR groundhog stakes - I think the shorter BP ones are fine. I have both, the monsters for car camping, shade tarps, etc, and the smaller ones for BP. Take 8 - 3 per side and one for each end. The total add weigh will be a few ounces, but 8 will tie down anything in any wind.
(b) Always have at least 10-12' of paracord 550 with you (two 6' lengths). And KNOW how to tie a taut-line hitch - forget line-locs, etc. If you have to configure something quickly on the fly, or alter the config, you need to know how to tie off guys in seconds. The 550 is for the two ends - worst comes to worst, these lines will hold.
(c) Take a tarp that is slightly "too large". I can squeeze into a 6x8, but I carry an 8x10. I'm 6'2", so my feet hit the end of the wall in a 6x8 (even diag). If I want to completely close down the tarp, and stay dry inside, then the 8x10 does the trick.
(d) Play around with different configs in your backyard. Know how to set them up quickly. The elevated A-frame is great when you want a sun shade - add 3' guy stays to each side. But knowing how to create an open half-pyramid, or really close it down if needed, should be a priority.
(e) I know it's overkill, but I carry a PU nylon rain hoodie. The thing not only blocks all wet, but also works as an insulator. Just know that it doesn't breathe, which may not be a concern if you hunkering down.
That's about it: perhaps an increase of 8-10oz+ to provide a pretty reliable, almost bomb proof weather system.