Currently sitting with my main party of siegfried at lv 93, vera at least lv 97, oalston at lv 94, laka at lv 96, i recruited all characters and all of them are in the middle range of 80-90 except oliver around 70 since i recruited him too late (ops).

I just beated diabolos and something tell me i'm getting close to the endgame/point of no return, so i have some questions about side quests i know exist but i don't know what they are for/how to solve them.
1-Simple and straight i have 0 clues how to open the door at hillsdale that was lysha's home i think, i already did ami quest with lysha and etc i thought that was gonna open the door but apparently not? interacting with the door using ami also didn't do anything.
2-I found some random memoir pages across the game and i have no clue what they are for, or if i even have all of them or where to find them, (Currently sitting at 8).
3-I have no clue what is the deal with kokkol at all or where to find the vomammoth fang and the other ingredients the  guy at a station ended up asking (which i assume is to forge some strong weapon).
4-i have no clue how to climb up the babel tower, is it connected to the story, or am i missing something? alongside that i have beaten 2 weapons/got 2 weapon fragments from omega and diamond weapon, anymore weapons i can do right now?
5-i currently am sitting at 46 marks i even did a map thing to mark the towns i did the marks already and the ones that don't have marks, did hunter's hq marks too and etc, if i'm somehow missing marks amount please alert me.
6-i been finding a bunch of bosche procure relics, i have no clue if i got all of them or how many of them there is (and is there even a way for me to check what is my current amount of relics got?)
7-i never found what the flan key item that i get from stealing from flans is for.

this is basically all i can think of right now in terms of sidequests/side content, i technically did some other stuff like the edea's tome, all dragons and etc, but still if you think i'm missing something please do alert me.

i do want to point out that i technically don't have adder since my save is corrupted so it leads to branch castle time travelling me to world 1, so if there is any major sidequest that requires adder i can't really do it.

1. Find Ami's best friend Nero in Merged World on an island with ice; it's the only solitary one with a house.  Use Ami as the lead to trigger the key event.
2. You will get the best relic once you find ALL 20  Memoir Pages (12 from Gaia, 8 from Merged world), then talk to Mid in Branch to trigger the event.
3. Kokkol (see Memoir Pages), regarding Odell Station man: find Vommamoths and get the fang drop, fight drill looking machines in Kasion Tower to get the ore drop and lastly you will get the Pure Nethicite in story mode treasure chest where Topaz Weapon awaits.
4. Babil Tower is story-related; complete the story more and it becomes open.
5. Revisit ALL the towns/villages with the CLAW insignia for marks. The fights are manageable if you're powered up.
6. I have no answer because I don't use Bosch.  He's just comic relief filler to me.
7. You can sell them for 500gil each.