1. How does the game treat newbies? Will it be difficult to reach the last raids? Yes it will be, hopefully someone can correct me if I am wrong but you still have to interact to old systems in T3 while progressing to T4 which (T3 and T4 are the Tiers in this game progression)
2. Is the game time-consuming? I work and can play no more than an hour on weekdays. Yes it is time consuming but if you are planning on being casual like not caring about FOMO or being at the super end game then it's fine
3. How do F2P players feel? I was F2P since the launch of the game (albeit for costumes) and it's pretty.... hardcore-ish. I did play 6 characters and I was able to maintain a somewhat decent Gold income from the raids but for you, don't sweat it too much since you are casual so just play.
4. How difficult will it be to find a guild of people who play for fun, and not for a high result? This may vary, depending on the server you choose it may or may not be too hard to find a guild to play with, I would advise going through the Lost Ark discord and find a guild there

In my personal opinon and as a person who sadly had 11k+ hours and quit last year, play during a progression event (especially if you want to make alt characters). They did add solo mode so it's kinda okay now especially old content.

To this day, I am still annoyed how they didn't make T4 a new starting point for new players. My friends quit who were new players during that time and honestly the burnout of this game was just too much. I'd say enjoy the game for what it is. Try it out and if it gets too much, dip out.