Do you need to complete a TR Visa before applying for a Certificate of Entry (COE) to Thailand?

Yes

If that is how you plan to enter Thailand (i.e. enter using the TR Visa) then yes. You need to be able to upload a copy of it on your COE application

According to the Thai Embassy Canberra, if you're from Australia, you are granted a visa exemption for 45 days , if you require more 60 days, you must apply for a TR 60 days. Then apply COE

Yes for TR

It may depend on how many days you want, 30 45 60..best to check this.

You only have 2 options with COE, as Stuart mentioned.

1) Apply for a visa, send off your passport and receive it back, and then you can start the COE process. One of the first steps of the COE is to upload your visa, so without that you cannot even begin.

2) If you are eligible to enter on visa exempt, you don't need to worry about the visa and can use that program and can start your COE without concern.

Depends on your nationality. If you’re from one of the eligible countries for visa exempt then you don’t need a visa to enter Thailand and can apply for a certificate of entry without. If not you need the visa before applying.