Modern era and beyond

I have a major case of restartitis and I havent been playing the game for very long. Due to those factors I have never actually made it to the modern era before until last night. In my first modern game I encountered ideologies, advanced warfare, and ai desperately trying to win. I have a few questions because I feel like a huge noob right now.
Firstly how big of a deal are ideologies? How can they help me, and what are diplomatic repercussions of selecting each one? Is air superiority a big deal? I found that bombers didnt do a lot of damage so is it worth my time? Finally I noticed ai going crazy right before I was about to win with wars, and trying to steal everything they could from me with spies.
Any help is appreciated, Thanks everyone!

You need to play a few games through to completion and you'll answer your own questions. The game used to really stagnate as you got closer to the endgame, I find that the changes from bnw make it much more interesting now.

Ideologies trump just about everything in Modern era.

To keep an AI on good relations that has gone a different ideology pretty much requires that you have freed their captives earlier in the game.

Conversely, about the only way relations with stay bad with an AI if you both have the same ideology is if you earlier in the game declared war on them. (Even the denouements will be forgotten when they expire.)

Since most of the time you want to choose the ideology that you think will benefit you the most rather than having one forced upon you for diplomatic reasons this means having a military good enough to defend yourself.
Similarly if you want to avoid having an ideology forced upon you due to influence concerns you need to build guilds so that you reach exotic with the other AIs, which only requires your tourism over them to reach 10% of their culture. In addition, great works is actually a major source of culture.

If you are the only civ with aircraft, you don't need fighters and can get by with bombers alone. But if they have aircraft then you need some fighters yourself for air sweeps. Both of these require Oil (as does Modern Armor and Battleships) so choose wisely.
Most players give Bombers Anti City promotions and concentrate on enemy cities. Ideally the city should already have at least an armory and Heroic Epic.

Have a spy present in your capital, build a Constable and Police Station there, this will cut down the enemy spying rate. (Normally your capital is the only city the AI tries to spy against) Later on you can build Constables & Police Stations in every other city of your empire and build NIA to both get an extra spy and promote all spies.

I believe ideologies were introduced in order to limit peaceful endgames. If an AI has a different ideology to you, it will induce an unstoppable genocidal hatred.

The AI will never forgo the early adopter bonus, so if you're the first to pick an ideology, you can guarantee that the next two civs to get ideologies will hate you more than the devil himself for the rest of the game.

Most of the effects of ideologies are pathetic, so there's really no point in getting the bonus ones; I'm considering switching up my strategy to deliberately delay getting to modern as long as possible, so I can pick the ideology of whatever civ I least want to war against. It's annoying, because there are other reasons to want to get to modern as quickly as possible, and I dislike perverse incentives like this.

Overall I passionately hate the ideology system, and feel it is easily the worst feature of Civ 5 and seriously detracts from my enjoyment of the game.

Ideologies came up because most people usually went to war so artists and musicians made many forms of social movements at home so that the war that was overseas or in a faraway land could cease. In civilization ideologies have tourism as the offense and the old school vanilla social policy as the defense.