Honestly you can hold your taxes pretty firmly near their default rate or raise them a bit. True to life, people will always complain about taxes. You could lower your taxes down to 2% and people will still be complaining about your outrageously high taxes. When a petitioner asks you for lower taxes, you can and should show them the door. If money is tight, don't be afraid to raise taxes; it will stunt your growth a bit, but you can't grow if you don't have cash so it hardly matters. As with most Simcity games, the start is by far the most challenging part and a small city will struggle to stay solvent. You want to grow as voraciously as possible, because a big city can easily be profitable.

For public transit, subways are the way to go. Rail lines are incredibly efficient early on, but they scale terribly as your city grows. Rail lines have only limited capacity so as you continue to build up you will need to run multiple lines, and all the rail crossings that will entail will absolutely murder your road traffic. Subways are the only real option in the long-run. Strangely enough, subway connections to neighboring cities are also strictly superior to airports. They have exactly the same effect with lower cost, don't take up very many tiles, don't lower nearby land values, and don't cause pollution. It's actually kinda silly, but it works.

Now to address the late-game economic depression... the sad truth about SC3K is that there's an oversight in the way they designed the population demographics that makes retirees into economy-killing monsters. Basically retirees count as "unemployed" people, so even though you may have lots of available jobs they will depress residential demand and people won't immigrate to your city to fill those jobs. This can throw you into a permanent economic depression from which you have no civilized means of escaping. The only real solution is to lower health care spending every so often to purge your senior population.