Developing techniques involving Rodinal & Xtol???

I’m starting to develop my own negatives and have chose Xtol & Rodinal to practice with. I plan on staying with these developers for a while and really learn how to use them. I have a few questions about the development process and how it will affect my negatives.

1.How does increased dilution affect the negative? Higher or lower sharpness or higher and lower contrasts?
2.How does increased or decreased agitation affect the development of the negative?
3.How the processes of the combined techniques affect the negative?
4.How will these techniques differ with different film speeds (ISO 25 vs IS 200)?

I’ve read through the posts on Rodinal here on APUG and found a lot of these techniques mentioned, but the outcomes were often not explained. I’ve heard of people using high dilutions and semi-stand agitation (I assume this is a little agitation at the beginning, then letting it stand with no farther agitation until the end of development), like Rodinal 1:200. I’m really interested to know peoples experience with the previous questions. Is there any set “rules” that state higher dilutions result in an outcome of A or more agitation results in an outcome of B?

Thanks for all your assistance.

Regards,
Martin