Might I make a suggestion?
If you are running MAMP locally on your Mac then you can create as many MODx installs as you like. Save the MODx download folder and back it up. Label the archive MODxBase or whatever. You can then copy that into our MAMP htdocs folder as often as you like so long as you give that MODx folder a unique name each time. You can then do multiple installs for testing purposes.
I find its a good idea to create several test ground installs. On one of them you should try adding the sample content during the install. Leave one or more of your test installs with the default template. With other installs you can build your own template and CSS system.
The whole purpose here is to have several systems going that will allow you to compare code, snippet calls, chunks, templates, paths to files etc. Then as you explore each snippet or new building blocks you can carefully test them in different environments to get the hang of how they work and connect with the system. Once you feel comfortable you can then try your new learning section out on your "real" project.
Be sure to take Susan’s wonderful guest user system for a spin on her site at www.sottwell.com as that gives you a real behind the scenes look at how the system goes together. You might want to try some of Mary’s great tutorials at
http://codingpad.maryspad.com/beginner-tutorials/
Bottom line: unless you are very comfortable its best to take little steps to build confidence with this system. Don’t try to do everything all at once with one project site.
I understand your frustration: I have been there. I had moments where I wanted to throw my computer through the window! Often a good night’s sleep and a fresh attitude in the morning does wonders...
EDIT: one other thing. I find all the RTE’s are frustrating to use. But RTE’s like TinyMCE are not developed my MODx developers. Using them is limited. You are not going to get full WYSIWYG feedback as you work with content. Its best to move slowly, save often and check the saved document often in a real browser window. I find its also best to be VERY thorough with your CSS file. You do not want to be adding a whole bunch of inline styles with any RTE in my book. If you are using the pull down style tabs in the RTE be sure to check the generated code by turning the TinyMCE preview off. Quite often the RTE is adding unwanted tags etc.
As far as folders and pictures go I use three systems. All my site presentation images that get displayed with my templates go in my templates/templateName/images folder. All my images that I upload into content pages (some using the RTE image upload system) go in the assets/images folder. I then use a custom jQuerry system to display groups of images. These get dynamically added via the MaxiGallery snippet which creates its own gallery folder system within the assets/galleries folder. MODx lets you build your own paths to images as you see fit. But this system keeps my three categories of images separate without too much confusing image path configuration.