You can play with the mod universal choice descriptor. It can be downloaded from this website. It shows the pathing, stats gained, relationship status and other values you get when selecting a choice. I used this to play without a walkthrough and it has helped me create over 20 playthroughs. You can also use urm to search and change values. It can also be downloaded on this website
Now to answer your questions.
1. If Lena and Ian are in a casual relationship, you can still be in a romantic relationship with Alison and Lena can sleep around. But if Lena and Ian are a couple, that closes her romantic path. However if you mostly ignored Alison before getting into a relationship with Lena, Alison will make a move on you and you can cheat with her. A romantic path is implied here in the newest update but it's still early.
2. Getting with Emma at the club closes Alison's romantic path but you can still get with the Bimbo version of her in chapter 11.
3. Yes it is possible to be in love with Ian while still seeing Axel. To do this, after sleeping with Axel for the first time, choose all the bottom options when thinking about him. Don't masturbate to him, ghost him, be rude to him. At the club in chapter 11, axel_desire should be false and you can reject Axel. Axel will call Lena in chapter 12. Agree to meet him. Respond positively to him and fuck him. Follow the normal romantic path with Ian and Lena and Ian should gift Lena the necklace.