You can apply up to 90 days in advance for your SE tourist visa as it's valid to use for 90 days. The multi-entry tourist visa is valid to use for 6 months from it's issue date.
You wont get a Tourist visa until Tuesday(in Laos) or Wednesday(in Cambodia). Embassy/Consulate closed at the weekends. Processing time 1 day in Laos, 2 days in Cambodia
If you're currently on a visa exemption then you first need the non imm O VISA before you can apply for the 1 year extention of stay. The main thing you need from the bank is proof your 800k funds were transferred from abroad