No - Not true at all for a Multi-Entry Visa (if the Visa is still valid - not reached the Expiry date) The whole purpose of a Multi-Entry Visa is just that... Example: First year of an O-A Multi-Entry Visa has unlimited Exits and Reentry. Exception for Everyone is under Covid-19 Restrictions the Thai Border is closed. A COE Certificate of Entry must be filed for and obtained. But a COE is Not the same as a reentry permit.
No - not an alternative. The WP. 3 is an Application to obtain a Work Permit. The WP. 3 must me filled out - Taken to the Ministry of Labor (usually by your Agent)... filed with a fee paid... stamped as successfully received and returned to the Agent. The WP. 3 then has to be accompanied with a Labor Ministry transmittal letter signed by Labor Ministry officer.
A very high speedHome Fiber Internet Router with AIS is less than 600 Baht a month.
From Lazada you can buy 4 G devices that use a SIM Card. Some are totally portable with a battery - some wired electric only. 700 to 1400 Baht.
Mobile Phones (term used here in Thailand) are available with Two SIM slots. You have to use two different numbers. One SIM is always primary for 4G Internet Connection.
In my opinion the usage plan you described is off target and buys you little at high expense. Phones can be set for auto change from Home or any WiFi to Mobile 4G. You can have maximum speed with my suggestion at an overall lower cost than your proposed plan.
- Please believe me - I'm trying to help you - not lecture you. The Agency you used for the O Visa and One Year Extension of Stay used a northern Immigration Office. To get another One Year Extension you have to use that same Northern Immigration Office and likely will have to use the same Agency.
If you quickly establish a new address when you are able to get back to Thailand - you could theoretically go to the nearest Imm. Office - file a change of address form and use that Imm. Office. Please note one does not "renew" an Extension of Stay. Basically you apply for a new one all over again. But you should not have to get a new Non Imm O 90 day Visa because it is there in your passport on a page or so before your current Extension of Stay stamp. Also it is normal for the Extension stamp (sort of rectangular) to NOT have reference to the type of Non Imm Visa it is based upon. Because that O visa is in that previous stamp I mentioned.
Every Extension of Stay is based on a Non Immigrant Visa which existed prior. The 3 month extension you got for your 30 visa was in actuality a Non Imm O Visa 90 days. Which some Thai Immigration Offices are authorized to issue.
The Non Imm O-A Visa is not / is never issued inside Thailand. The O-A Visa is Only Issued at a Thai Consulate or Embassy in a country outside Thailand.