Hello! I was in your position not too long ago, and right now on my way to my third immortal victory, with the advice of many helpful people on this sub.

The general rule is that Science is everything. Anything that contributes to faster science is good. So population growth and the happiness to sustain it, and buildings that increase science, research agreements. All these are very good.

I generally prefer to go liberty, with tradition being a second for most play.

Tradition is better in most situations. It's a much slower start (which I dislike), but it rapidly outpaces Liberty as the game progresses. Rationalism is a must. Start Rationalism as soon as possible, although you have some flexibility in when you choose to finish the tree. When it seems you can go wide, or when you definitely want to go wide, Liberty may be better.

Tech: I tend to get whatever opens up my luxury resources, followed by writing into drama and poetry (for the culture). After that, I just sort of seem to lose a bit of focus. I go for whatever tech solves my immediate problems, regarding defense, money, and science. When I hit the renaissance, I almost always go straight to industrialization, to unlock coal and then to get three factories for ideology. Order is vastly preferred for me.

Prioritise Philosophy for the National College. Science is everything. Nothing wrong with heading straight for an ideology though.

Cities: I tend to build up to 4

4 is fine, but don't lock yourself down with a fixed number. If there's a good city spot, go for it.

Diplomacy: I barely interact with other civs, unless it specifically suits me. I let them make the first move, because I'm lazy and they all are out to screw me in general anyhow.

Bribing civs to go to war with each other has been key to all my immortal victories.

That's all I have now. Hope it helps