Welcome to the forum!

  • Weapon-wise, I have an industrial metal dustpan that I'm planning on using as a scoop. I also have a scooter motor for an axe (mostly so I can say it is the best thing since sliced bread, I'm doing this for the puns really), but I'm not sure if I should walk before I can run and focus on just building something that runs and pushes for 3 mins. However, adding the bulkheads for an axe mechanism would make more much needed space inside the robot, as I could mount the motors under/through the bulkheads.
Yeah, I would get something moving first and then get a weapon in. Surviving 3 minutes in the arena is an achievement on its own. Yes to planning ahead though, never hurts to do so.

  • Battery issues at the moment are that I'm rather nervous around Li-Po batteries as a first time builder. No doubt I will take the leap eventually, but testing with the drill batteries first seems like a good plan.
Nothing inherently wrong with drill batteries though it is worth noting if the batteries from the drills are Lithium batteries as well as there are some extra rules surrounding the use of LiPo (note: not LiFePO4 batteries) in fighting robots, it is worth checking the rules for these and build with them in mind (again, forward planning). The only thing I can think might be a problem is the battery capacity but for a relatively simple robot, this is unlikely to be a problem.

  • Toaster is too small and obviously not suited to robot combat. Any suggestions to help reinforce/expand this would be appreciated.
Well you realised this before going in, better than my first robot with a lampshade as a shell. I would cut slots into the toaster and mount HDPE panels to it (you can get this from directplastics.co.uk) lengthways for a frame and then extra HDPE around the sides for impact absorption.

  • I cheaped out on the transmitter I bought, not sure if it is suitable. May buy another of the more commonly recommended ones at a later date.
I've used a variant of that transmitter before on a Beetleweight robot, it is OK. You'll find that the Sabretooth will do the channel mixing for you to give you forwards/backwards and turning on both motors but if you wanted to use different, single channel ESCs, you'd need a transmitter with mixing on it, such as the OrangeRX transmitter.