I followed a sample from the internet. It should bear a corporate letterhead, your name, passport number, title/role and stating "Remote Worker/ Freelancer", corporate stamp and signed by HR or director. (Disclaimer: This worked for me in Jakarta, I can't guarantee for other Embassies.)
No need to book an appointment at Jakarta but need to book an appointment at Vientiane.
At Jakarta, the standard processing time is 3 working days after submission. You can count the number of days (include weekends and public holidays), easier for you to book the return flight. I.e if you submit documents on Monday, your passport can be collected on Thursday. Submit on Tuesday, collect on Fri.
At Jakarta, neither Thai lease agreement not TM30 is needed.
:Which embassy did you apply at? I don't think my clients were contacted, though their email or phone numbers were listed in my documents. If anyone were contacted, I would be informed.