What do you mean by 'basic Kitas'? Retirement?
Initially, I was using an agent when I moved to Bali, but eventually, we just started doing everything ourselves. Or I should say, my wife just everything and I occasionally went in for photos/fingerprints.
I found immigration to be quite helpful and you can go in there and they will tell you all of the documents you need. You need to give the same documents to an agent, so there is no difference. They may come to your house for an interview, so it is good to make sure you can remember dates, like your anniversary and so on.
There is some good info here also to get started:
https://www.expat.or.id/info/mixmarriages.html