I don't have any experience when it comes to being a graphic designer but I do have experiences with other things that might help you in the future.
1. How do you talk to clients online?
When it comes to talking with your clients online you should be professional and courteous at all times. Listen to the client's concern and address them in a constructive manner. You can use tools to talk with your clients like video conferencing and screen sharing to have a better communication, be transparent and honest. Also provide regular updates your progress.
2. Do you sign papers for online clients? or wala po? if wala whats the scenario or anong ganap na dapat professionally ?
There is no such thing like online siging of papers specially here. Just communicate and if you come up with a deal then that's it, but before going to a deal you must give your conditions if you any.
I'll pass no. 3 since like I said don't have experience with that.
4. Do you ask for a downpayment?
Downpayment is a must for me. You can have at least 30%-50% of downpayment. Don't offer you services for free, they may not continue on your agreement at least with downpayment your service will be paid somehow even if they don't proceed.