1. How can I make a Hyper Cube properly without having to give up a Hyper Cube setup?
Swap gems that're around the hyper cube setup in hopes of finding a lead into a hyper cube. If there's no gems around the setup to swap around, ditch the setup and give up on it. Don't stall the gameboard for 20 seconds in trying to get a successful hyper cube...especially on King.com. Keep your score moving by making cascades, along with creating & deonating power gems.
2. I'll speak on behalf of King.com's version of Bejeweled 2, as that's a version of the game that I'm pretty good at.
I'll actually blow up my power gems if I have 5+ more of them bunched together, regardless of what level it is...I'll even do it on level 1. Consider the "bunching up" of power gems to be a stroke of luck for you. Any time you can collect 5+ power gems together and there's no other power gems to collect on the board, feel free to blow them up. Once you play Bejeweled fast and have a perfect eye for spotting power gem setups, you'll be able to re-collect power gems and do another big gathering of them. Don't stall the board by trying to "protect" your power gems if there's barely any moves left. I'm comfortable with giving up 1-2 power gems just to get the board moving, or to move on to the next level.
If your power gems are situated at the bottom of the board, protecting them is easy since you have the whole top half of the board to play with. If they're taking up the center portion of the board, you'll either need to get the game moving using the sides of the board or figure out a way to bunch up your gems close for a big explosion.
My personal motto with Bejeweled is to keep the game going. The worst thing that can happen is having a board where you're making single swap after single swap. You need to be actively kicking butt!
Jacob, aka Meikyousisui on King.com & Worldwinner.com