every cent you spend on insulation will be paid back over and over in lower electric bills. its one of the places you should consider spending a bit extra on initially as it is harder to improve on later unlike many other parts of the setup.
I find kribs and angels do ok together if you don't mind the occasional nip at the angels fins (nothing major ime)
Discus will probably be a waste of money with angels.
btw as the GAE gets older it will try to take over the tank and may attempt to suck on the side of your angels.
I have found that my GAE does will with a Siamese algae eater as they constantly mess with each other in a more playful way and everyone else gets left alone
I'd avoid MDF as it may swell if it gets wet and crack your tank.
I don't see a problem using 2 sheets as long as there is poly on top and you try and get the 2 sheets level.
check the impeller is sitting properly and the rubbers on the ends of the shaft are not cracked or damaged. most common causes of rattles (I just can't be bothered fixing the old one)
hrmmmm... good intelligence hiding in a cave, bad intelligence running a petrol generator in an unventilated area.... who was the third party orchestrating it, those muppets couldn't have thought it up themselves
spent all day on the couch recovering from a bad KFC dinner, made very good friends with the porcelain goddess today and have an early start at work tomorrow.... not looking forward to it