Dear EMTSU,
In my case, the VLAN tag is configured in ONT where the fiber terminates. So it is not needed, but if your ISP doesn't support that, then you can do it in your router itself.
Idle time out is needed and in my experience, it makes sure the connection is always up.
My ISP didn't mention, what authentication they are using, so as per PPoe wizard in SRX there is an option to automatically identify it. I selected that, that's why both authentication there.
When I started to configure the first PPoE connection, I have gone through a number of different problems as you have experienced. What I did was, I configure my laptop as a PPoE client and directly connected to my ISP modem (bridged MODE) and check whether it is working or not, If the PPPoE connection is working with my windows machine then the ISP side is OK and your router configuration is to blame. Please go through the below link to configure your windows machine.
https://helpdesk.voyager.co.nz/index.php?/Knowledgebase/Article/View/222/49/ufb---pc-to-ont-isolation-via-pppoe
Please also let me know what error you are experiencing while configuring the above link.