1. there is a lot of tutorials, maybe can read if u are using Chris Translation, but the info are already well enough https://llchrisll.github.io/ROTPDocs/guides/basic_custom/
2. there isnt. you might need to know which npc was there, or not and disable it. Maybe some changes too outdated one too if going to old episode.
3. conf/battle/ you might see most configs there.
Depends on how do u want it. download new and start fresh.
OR
You can also update your rathena and also all related databases to match to latest rathena.
Note: The new skills of Dragon Knight (Dragonic Breath), Biolo (Explosive Powder, Mayhemic Thorns), Meister (Mighty Smash, Spark Blaster, Triple Laser) need a client 20220602+.
I think what you use is client 20220406, which is April 06, not June 02.
u are using palette from who, and did u read the required files to use that palette ? doesnt need those patch though.
If u didnt, read back what the required files from the palette.
Since I got a few request to add shadow weapon or costume weapon part (which weapon part is already exist), Ill add it soon but it might need src mod to make it appear in a client.
I wont support that src mod part so you might need to make it work yourself.
hmm. I didnt remember I get this issue. What I remember, the client wont open at all at windows 11 if sclientinfo or clientinfo have issue.
Have you tried check that ?