Note: I'm pretty sure my take on Hyperspace doesn't jive with canon, but I don't care.
1) Is travel in hyperspace in straight lines only?
Basically, but gravity bends that line. So your route might pass through a star system and curve a bit, and that's why you gotta pay attention in Astrogation 101.
2) Can you change course while inside hyperspace?
Nope. You can stop early and recalculate though.
3) Can ships inside hyperspace detect each other or see each other if sufficiently close?
I like to think that a ship traveling through hypserspace leaves very small ripples in spacetime which can be tracked. If you're chasing an enemy ship that jumps to hyperspace, you can try to tail it. Your ship needs to be about as fast, have good sensors, and a good Astrogator, but it can be done. If you're not attentive, and are two seconds late dropping out of hyperspace, congratulations, you just overshot the mark by about two million kilometers, and he's making his getaway. As for seeing him, no.
4) Can ships inside hyperspace communicate with each other? With people in real space?
Nope.
5) Can a ship in real space detect a ship in hyperspace that flies by it?
I think I would put this down as theoretically possible, but never happens. Things in space don't tend to pass close by each other. Here on Earth, we recently had a "near miss" with an asteroid that was 15 million miles away. Whew, that was close.
6) If ships in hyperspace are very close, can they shoot at each other? Use tractor beams? Splice?
Nope.
7) How long does it take to go from one edge of the galaxy to the opposite edge? Hours/Days/Weeks/Months/Years?
Just shy of Ludicrous Speed
8) Can droids crawl around on the outside of a ship in hyperspace ala Phantom Menace? How about people?
Yes, but seriously, make sure that tether is secure!
9) Does gravity itself cause a ship to revert to real-space? Or can a ship actually crash into a planet?
I'm of the opinion that gravity plays hell with the hyper-phase state that ships enter when they jump to hyperspace (technobabble incoming, Captain!). Flying too deep into a strong gravity well will start to rip the ship apart as it damages that hyperstate. Enough damage, and the ship will be ripped out of hyperspace, and in a very bad position, probably hurtling directly into a planet or star. There are safeguards on the ship to pull it out before any of this happens, and Interdictors largely rely on those safeguards to catch ships. So smugglers who knowingly fly interdicted routes might tweak or even completely disable those safeguards for such a run. If they're fast, good, and lucky, they might be able to pass through an Interdictor's gravity well without sustaining too much damage. If it was a planet, well, nice knowing you.