Hey Julius:
Yes, you mentioned a bit about the difficulties you experienced. Its always a struggle I think, but it does seem like you have had an extraordinary difficult time of it. The good news is Modx is very good at helping your SEO, and for pictures you are going to want to use good file names and maybe later some tags.
Let me ask about the html files with inline css, the files are still available? The question is, do those html files have things like the header and footer in them, or just the contents of one page.
The way it usually works with Modx and its the normal way generally, is the stuff like the site header and footer and so on, usually including the top navigation bar, are put into the template, this is better because if you want to change the footer, you can change it in one place, rather than going through every file and making the changes again and again. I remember in the old days that's what they would have to do, go through each page to change things.
When we do it this way, you will use a code like this [[*contents]] in the template, and that is the place where the template will pull that resource's contents into the page. If I have a resource that has one sentence, 'nuan is cool', but do not have the [[*contents]] in the template, that sentence will not be in the page, we would only see the stuff in the template itself.
Now if the page is unique, then it can all be in the template, a resource is still needed but it can be blank. I also think the opposite can work, with a template with only [[*contents]] in it, nothing else, and all of the <head> content and everything else in the resource. So that's the flexible relationship between template and resource (page) contents, and its just according to your needs. The [[$chunk]] code you've already seen is another part, with the same intention of putting key code in one place.
So the question about your "html pages" is what the html looks like. If its got stuff like the header and footer, that's fine, you can display it easily in a resource (with a [[*contents]] template), but it will be hard to change, and the way to "fix" that would be to cut out the footer contents, put it into the template, and then delete the footer contents from every page...which could be done with a batch command I believe, not my area though.
You can understand that chopping up the files may be tough. And in-line css, while I use it a lot, is precisely not portable or easily changable.
So, you may have to consider what bits need saving and how to do it.
