Actually if you provide a travel date more than 3 months out from your application they won't process it, but once you have been issued the DTV you have 5 years in which you can enter.
DTV_Begpacker you get issued a visa for the purposes you apply for the visa. There are 3 purposes you can apply for - workation, soft power, family.
Compare what you have just said to a Non-O visa, it has many different purposes way more than a DTV but you can't apply for one reason and use it for another
you won't get a DTV based on workation if you don't have either revenue or provide a clear plan to attaining revenue. The 500k baht requirement is looked on more as an emergency fund, so they want to see how you will support yourself
it doesn't matter where you are working. Thailand treats online visa applications in exactly the same way they did when you had to attend in person and hand over your passport and application. It's just that now you hand them over electronically