For marketing, you can do many things, but it comes down to what works for you.
You like tweeting things about your comic? Get on twitter and start sending out tweets. If you like talking about how you make your comic, make a YouTube channel. Like to colab? Find people on forums (like this one!) and see if anyone would like to make something with you.
Depends on how active you want to be marketing yourself. All that matters is that you are putting your name and the comic's name out there.
But you can also just let your comic grow organically. If you make good content, people will start following you and sharing it among themselves. If you find yourself on the creator spotlight or even just on the fresh page of TAPAS or Webtoons, you will get people just checking your work out just cause you on those sections.
As for a buffer, it depends on how quickly you can work I guess. I know of people who have no buffer and just smash out the comic when they need to, but they have a very simple style. Others would do what you are doing and have a large buffer just in case.
There is no right or wrong way to anything in regards to anything you do with your comic. Just do whatever makes sense to you or is the easiest. And don't be afraid to change, since we all change all the time.
