Nice to get a mention by name! Just so the ripping and tearing doesn't happen, here are my suggestions:

* Chains VS belts is an endless debate and mostly down to personal preference. Chains are always going to be heavier than belts, which means lightening up the frame or armour. Belts are usually bulkier (wider) than chains. Belts are more fussy about the correct tension than chains, but adding a tension adjuster is easy and helps prevent both belts and chains from falling off. Chain length can be adjusted with half links and a tool called a chain breaker, while belts are a set length. You can get around length issues with a larger tension adjuster wheel. My personal preference is belts, but only by a small margin.

* I don't have any experience with the Sabertooth ESCs, but have heard more negative comments than for the TX85a controllers. There is plenty of community support for the Botbitz ESC, which can be hugely useful - you can often buy or borrow one at events, something that won't happen with the Sabertooth ESC.

* The Colson wheels are a great choice, you won't regret it! Have you thought about how to attach the sprockets or pulleys to the wheels and what sort of bearings to use?

* With the connector choices, it sounds like you are trying to avoid soldering. Its a good basic skill to have and almost impossible to avoid when building bots. A soldering iron with an 80 watt rating is the perfect size for connectors and power wiring.

* I don't see a fuse in the circuit diagram. Soldering a cut-down car fuse to the back of the XT60 power link is a convenient and space saving place to put it.

* HDPE is never a bad choice for a frame, look at barrel bolts and tee nuts to hold everything together. Sheet metal screws are OK for holding internal parts to the frame, but will not stand up to much of a beating when holding the frame together.