If you decide to try out creating mixed media pieces here are some tips I've figured out:
Solvent based markers (like Prismacolor) make a great base. When using dry media, like colored pencils or chalk, even the most careful artist can leave tiny blank spots. Putting down a layer of marker can help prevent that and give you a base for where you are going with color palette.
Acrylic paint is just about the only thing that will stick on top of waxy colored pencils (which is probably the kind you are using if you want it to blend properly) and cover them.
Chalk is great for smoothing things out and adding that soft filtered look over color pencils, paints, or anything flat. However, it will fall right off, so stick that finished piece in a frame right away! Using a spray sealant always sounds like a great idea. In my experience spray is the same as wind, which is chalk's natural enemy.
Markers and watercolor paper aren't the greatest mix. You'll end up using quite a lot of chalk to soften up the lines and the ink doesn't like to get into the divets. Better to pass on this combo. If you do choose it, plan to spend time cleaning it up in Photoshop for any scans. It can look pretty good in person, but the scanner will find every little flaw.
Blank ink lines can take a piece from being almost there to finished. However, if you are doing the black lines last (as I usually do) be incredibly careful that you don't touch them if they are over colored pencil. Don't be afraid to twirl the paper around so that you don't touch your lines. Covering finished lines with a paper works for some people. However, you should be careful not to drag the paper across your piece or you'll smudge it anyway. I prefer to twirl instead of cover. I like to be able to see the thickness and style of the lines I already laid down so I don't start with something different.
An acrylic wash on paper is not the same as a marker wash. Marker is easily covered by ink, pencils and softened with chalk. Acrylic can show up through pencils and chalk.
Chalk is always the last thing to put down. Unless you enjoy messing up your markers, brushes, pens, etc, put the chalk down very last. Chalk wants to stick to your wet media way more than it wants to stay on the dry paper/canvas.
Watercolor paints can be great. Depending on the concentration you can do light colors to very vivid. They will go over just about anything and with practice you can get them to be thick enough to even cover pencil. However, watercolor paper exists for a reason. It doesn't curl. It does have texture and soak up way more media than a smooth thin paper. Thin papers work with watercolor, but your piece will curl. You can avoid this by taping it down while you work on it.
That's all the random stuff I've thought of recently. Now back to laying this white ink over marker on bristol paper before finishing it with pencils and chalk ;)