Hi, I'm the GM and I came across some things that I need to know...
1) Mostly, this detail about the world lets you, as the GM, limit communications between different planets however you feel like.
If players need to find information about a specific individual they'll either have to know it themselves with an appropriate Knowledge check if the person is particularly well-known or with a Streetwise check to ask around. Since this is a collaborative narrative game, let your players come up with how they find that information out. Maybe they flip a Destiny Point to know someone with limited access to the Holonet. Let them do some sort of social skill check (Charm, Deception, Streetwise, etc.) to arrange the deal. Maybe there's a complication like a personal betrayal in the past. Maybe you can work Obligation into this somehow. Maybe they roll some Threat or a Despair and create potential complications in the future.
2) Up to you. You can get some ideas here:
3) Since the Holonet is restricted, it will be very difficult or impossible to communicate in real-time between planets with a holo-messenger. In A New Hope, Princess Leia uses a holo-messenger in R2-D2 to relay a message to Obi-Wan Kenobi but R2-D2 has to deliver the message personally. Use that as your guide.
Here, again, you as a GM get to make things as difficult or as hard as you want them to be. If it doesn't matter how the players deliver the message and they want to transmit it in real-time over the Holonet, it might be more fun if they slice into the Holonet but this should be it's own encounter in an of itself since they'll probably have to break into a place that can access the Holonet, deal with any Imperial presence there, and not get caught slicing into the computer terminal. This could be a good way to increase any Criminal obligations if they get caught or if there are any complications.
4) The game assumes you'll do what makes the most amount of sense in any given situation. If the PC is behind a solid duracrete wall and firing a blaster through a narrow opening, you can add two Setback dice to attacks made against them from enemies on the opposite side.
If there is no line-of-sight, then you can't make any attack so cover doesn't even apply.
5) What do you and your players want to have happen? Remember, the lowest total Obligation that a PC can have is 5. Maybe they pay that one debt off and reduce their total Obligation to 0 and remove the Debt but maybe the debt-collector gets greedy, thinks that if the PC was able to get the 10,000 credits to pay off the debt that they can get more credits and now they get a Blackmail obligation. Maybe the PC paid the debt off late but the lender forgives them in exchange for a Favor obligation.
Most importantly, you should talk with the player and you should both come to an agreement on what should happen.
6) Very likely, yes. That's a rather reckless method of property destruction and depending on who owned that building and how many people were murdered in the attack could mean all sorts of consequences from being hunted by local authorities or a crime syndicate, having a bounty put on their heads, or even Imperial involvement.
7) Generally, my personal style in non-structured (non-combat) game play is to only allow a single skill check for a particular situation. If the PCs are sneaking, they get one Stealth check. If the PCs are searching for something, they get one Perception check. The results of failure depend on the situation. If combat is imminent (the PCs are trying to sneak past some guards) then failure means initiative begins and attempting to roll Stealth again would just be a waste of a turn when they should be diving for cover or returning fire.
Most commonly, I'll have players that keep rolling Perception until they find something in the room. If there is a specific item that they PCs are meant to find and they say they look for it, then they simply find it. No need to roll dice, just give it to them. You should only roll dice if failure means something interesting happens. If I wanted something interesting to happen, I'd call for a single Perception check for the entire party using skilled or unskilled assistance and I'm mostly using the results to narrate how long it takes to find the item (if time is an issue) or what else they find in addition to the desired item. More success means perhaps they find another useful item. Triumph might mean they find a key bit of information or an item that makes a later encounter easier. Advantage might mean they find what they need quickly. Failure would just mean they only find the one item needed to move the story along. Threat might mean it takes longer to find the item and the PCs take some Strain damage. Despair might mean they trigger a silent alarm and guards arrive right as the PCs are about to leave.
For your scenario, they attempt a Stealth check, fail, and then if try to Stealth again it wouldn't really matter. If they failed and the bad guys are on the way then the bad guys are still on the way.
8) What 2P51 said above.
9) If a PC is firing a blaster pistol at a ship or vehicle that has no Armor, they would have to do over 10 points of damage to even hope to cause any effect. The PC would have to use the Aim maneuver to target the specific cannon on the ship and have two Setback dice (rules on page 201). If they spend two Aim maneuvers, they would only have a single Setback die. If they did manage to score over 10 points of damage, I'd let them temporarily disable the component with three Advantages or disable it until repaired with a Triumph.
10) That is up to you. You can also use it to apply Setback dice to the enemy.
11) Only if you can buy it. It's a restricted item and likely illegal on some worlds. A thermal detonator is also more likely to destroy the entire room or the part of the building you're in. It's a bomb and not something you want to be anywhere near when it explodes.
12) If the PCs are making an ambush that the enemy is unaware of and can control the terms of how the combat begins, then it is a Cool check. In nearly all other situations, it is a Vigilance check.
13) It depends on the ship. You will have to make a decision based on what makes the most sense.