Don't be sorry about the questions! Its awesome that you think I am knowledgeable enough to answer them for you.
The reason I put cories instead of rummynose because cardinals and rummies school kind of on the same level in the same kind of way. Plus they both have red in them. So cories dwell the bottom and keep the substrate fresh and turned over and add another dimension of fish to the tank. But really for your main schooler you can choose rummies or cardinals, whatever you prefer, then add a school of cories instead of another tetra. Which looks better IMO.
2 GBR or BR(same thing I think?) is what you should put in a 29 because they are cichlids who do well in a male-female pair and fight with other pairs unless your aquarium is about 50 gallons or more. This is what I would do for a centerpiece.
Not sure about the Hatchets. Stock them at the very END and decide if they would be a good choice for your tank. Also stock them last on aqadvisor and see what it says. They are great jumpers and might want more room than a 29g. Not sure though.
Clean up crew would probably be amano shrimp. They are awesome. Maybe add some nerite snails for the glass too? But i never owned nerites so I'm not sure.
Hope I helped a little.