John Thomas

Dtac has been good for me and you can keep the number alive for one year for 30 baht even if you don't use it or top up. Once you come back, you just add another 8-15 days unlimited package or whatever. So you keep the same number always.

I got an older phone that is 4G which is good enough but it is too old for e-sim

You could try Sing Sing Theatre, Sukhumvit Soi 45. 
I have been many times with LB'S and often meet with their friends there. Pricey but a great atmosphere.
Also BoBo, Hyatt Regency can be good with a few top shelf LB's there., 

I'm constantly amused by those who fret over how others choose to spend their money.

Made sense to me but for clarity, "other" friend refers to any of your friends on your Line app, not a specific friend called "other".
Yes, I have two phones, one for personal/work and another for Thailand. I can transfer the line id between them as per my first message. 
I am sure it will work with two sim cards on a dual sim card phone or with two interchangeable sim cards.
 

If you have "other" friends on your Line account you can share the contact with your "other" friend. The "other" friend receives the link from your Line account. The "other" friend can then let you know the details.
This is the only way  you can find out the Line ID of a friend if they are not already in your phones' contact list.
I hope this helps.
 

If you have "other" friends on your Line account you can share the contact with your "other" friend. The "other" friend receives the link from your Line account. The "other" friend can then let you know the details.
This is the only way  you can find out the Line ID of a friend if they are not already in your phones' contact list.
I hope this helps.