Welcome to the forum. And thank you for supporting this site.
If you are new to this game. Just play, and you will see what is best for you. It takes time (not much - trust me) but soon you will get used to this game and all the mechanics inside.
ad.1 Flight model difference - yes and no. Depends on point of view. My personal feeling - it is not harder - it is just that the computer is cheating - and reacts faster, and can do much crazier things in a dogfight than you. Just that. But it is m personal observation. do like this....and check how it is going for you...
ad.2. Some ladies in some situations, can behave better with flaps for a short period of time...just a feeling. Play and you will see. It is not like you will crash...and cannot play again. Refly and you are good.
ad.3 yes it is hard to get used to it. Mostly because you can not operate the gunsight properly, but some small edit in avionics.ini can - simulate ccip in older machines.
ad.4 you can change settings anytime; you will see. For a start - put it on normal so you can get used to it.
ad.5. To play is to mod the game. Remember that you can change bazylion things in-game by simply opening the file in Notepad. And yo do not have to worry about screwing up. Just make a copy of the file you are trying to edit...and just that. IF you fail and do not remember what you changed, delete and bring back the backup. This is the only way I am doing when editing files - I do not have time to write back again - I just bring back the original and that is all (more or less - i have my way of modifying files - but since you are starting it is not important)
And on top of that - familiarize yourself with the game structure, how to extract files, where files are stored. Where mods are stored. And take it easy. It is a game.
And I said it many times. Many mods are quite old, but it does not mean they are bad. But with time some particular things in mod culd be updated, and released seperately. So back up your files, before "updating - overwriting," as you might make things worse.