This group is chock full of advice, examples and guides. If you can't find enough here to apply on your own, just pay one of the members with a successful application in your category to help you out. Don't support to expensive, scammy agents.
You can never do your first 90-day report online. So doing it online won't work with a DTV, unless you're extending and staying longer than 180 days.
And the 90-day report doesn't matter for you, if you're flying out soon. It is only important if you have anything to do at an immigration office. The immigration at the airports don't care about the 90-day report.
Anonymous participant if you APPLY for a visa and say you're going to fly more three months in the future, tour application will be denied. This is to prevent people from making the queues at the embassies even longer bu applying too early.
But nowhere is there a rule saying you have to use your visa within three months.