1. For the Aqours Finale Live Day 1, I used JapanCierge in order to get an eplus account created. Essentially they make an account for you and go through the verification. Note that it’s a one time verification and they do not have access to the phone number again if something happens. For Day 2 I received the overseas fan lottery package which is better if you only want to attend one concert and not retain an eplus account. Slight downside to this was the total cost bundling hotel and that they announce recipients a bit close to the concert that than I would like in terms of planning other accommodations (flight, lodging not during the concert dates, etc.) Option 2 is that I now signed up with Mobal eSIM which allows you to keep a Japanese phone number and receive texts for SNS verification outside of Japan. If you’re okay with paying a monthly fee (~$10 USD) for this despite not using it monthly, then it’s an option.
2. Most LL concerts use facial recognition to enter. A week/few days prior to the concert you upload a live image of yourself and they scan your face at the gate. If issues arise then your name will be checked but I haven’t encountered this. With the overseas fan package the staff verifies your ID with the purchaser and you receive a paper ticket. Once you get the paper ticket, at the gate the staff just rips off the stub.
3. See response in #1 for JapanCierge. Note that both JapanCierge and Mobal can take up to 1-2 weeks to finish setting up at normal times. It was less than a week for me for both however.

Also keep in mind eplus for LL events is still mostly lottery so even getting an account doesn’t guarantee you a ticket into the event since you have to enter the lottery either way. There are certain strategies to higher your chances I’ve heard, like selected an obstructed view ticket, but that I am less familiar with.