I don't see anything glaringly wrong with those development wise. Maybe a tad bit underdeveloped, but that's harder to judge from scans. The real test in my book for development is wet printing. If you can print a normalish scene with a normal brightness range acceptably on grade 2 or 3 paper, then your development is (approximately) good. If your results are too contrasty in those prints, then you need to reduce development. If they are too flat, increase it.

They also might be a bit underexposed. For example, in the EI 400 roll, frame 41 is definitely underexposed, and I'd say that frames 39 and 4 are too. Some of the shots, like 38, are useable, but in terms of the women's hair and clothes, you'd need more exposure to capture detail - so we could call that underexposed. A lot of your frames on that roll have that same look, but you were also shooting a lot of people with dark hair and clothes who are standing in front of bright backgrounds - a recipe for underexposure of your subject if you don't account for it.

The EI 1600 shots are definitely underexposed, but that goes without saying, since they are intentionally underexposed by two stops. This will cost you detail in the shadows. That being said, it doesn't look like these shots on the whole are underexposed any more than what was necessary for EI 1600, and the development doesn't look like it's under. It might even be a bit over...

Most of the time, unless you are really screwing up the development, problems with negatives are usually exposure problems, with a big tendency towards underexposure. While I do not belong to the group that says you should half the rating of any film for good negatives, you do need to be careful with your exposure, and note that negative film can handle a lot more overexposure gracefully than it can underexposure.

I would second picking up a copy of Horenstein or David Vestal's "The Craft of Photography". The latter is very good and available very cheap used.