It's a multi entry go and come as you please for 5 years read the conditions of your visa. You should know this information it's not rocket science FFS
You are free to travel as you want. But be aware if they ask you to attend interview you will have to return and risk being asked for your passport which the embassy will see you did not stay there. Your risk it's your money so do what you like
follow this as best advise. It embassy specific. Once you know the embassy you are applying at and the category you can then search in the site. You have to do the ground work yourself if you get stuck with specific issue then ask here. Everyone is the same but you work it out yourself it's not that difficult
Whatever you did for work or visits pre application is not relevant as long as you don't have any visa type that is not cancelled. Just apply submit the correct documents as asked by whatever embassy location you apply. If they have an issue they will request more documents and maybe an interview good luck
There is no such thing as paid in advance. You go to immagration 14 days before or 7 days after the date. It's free if you fail to report it's 2000 bht fine. Maybe you are thinking of an agent reporting for you they charge like 500 bht for the service
It's it a holiday or are you planning to move to Thailand to live. This visa is not required if you are planning a holiday you will get 60 days visa free on arrival. Your post doesn't give enough information on what you are doing married children yours all same nationally???