Spouse Visa from Outside UK - Doc upload and application submission

Hi everyone,
Start preparing for my wife's spouse's visa from abroad. Few questions regarding the uploading documents online and application submission please:

1. I will have all the supporting documents by the end of September so aiming for application submission in the last week of September. Can I register now and start uploading supporting docs now whatever I have currently? Is there any day/time limit to when I can start uploading documents?

2. I am assuming here documents can be submitted before the application submission? Is this correct? Is it acceptable to submit documents after the application submission? If I can recall it was some hours before the biometric appointment, is this correct?

3. At what point do I need to pay for the visa fee and IHS? Really looking for the steps of applying online here, please.

4. To get an appointment around the end of September how early the application should be submitted and how early we should look to book a biometrics appt, please?

Really appreciate it if anyone can help answer the above, please.

5. Also, I am expecting the last payslip to be received on 22nd September and therefore the transaction in the bank account. Is it ok to submit the application before 22nd and then upload these before the biometric appt considering we book that end of September lets say 30th of September?

Is this the right approach please or should I wait for payslip and then submit the online application after 22nd September?

1. I will have all the supporting documents by the end of September so aiming for application submission in the last week of September. Can I register now and start uploading supporting docs now whatever I have currently? Is there any day/time limit to when I can start uploading documents?

You can only upload documents AFTER you have submitted and paid for the online application.

2. I am assuming here documents can be submitted before the application submission? Is this correct? Is it acceptable to submit documents after the application submission? If I can recall it was some hours before the biometric appointment, is this correct?

No, you can only upload the supporting documents after you have completed and paid for the online application. You upload the documents before the biometric appointment.

3. At what point do I need to pay for the visa fee and IHS? Really looking for the steps of applying online here, please.

It is at the end of the online application form. You pay online.

4. To get an appointment around the end of September how early the application should be submitted and how early we should look to book a biometrics appt, please?

You can only book the appointment after you have completed and paid for the online application. The date of application is the date you submit and pay online, it is not the biometric appointment date. How soon after applying you will get an appointment, depends on where you are applying and the capacity.

5. Also, I am expecting the last payslip to be received on 22nd September and therefore the transaction in the bank account. Is it ok to submit the application before 22nd and then upload these before the biometric appt considering we book that end of September lets say 30th of September?

No, your supporting documents MUST be dated ON or BEFORE the date you apply online, which is the relevant date of application.