From experience of those whove built Heavyweight clusters before - its easier to build a single heavyweight.

Clusters tend to use the same components as main heavyweights (Ampflow motors, Bosch 750 motors, ect) however now your building 2 of them - doubling your costs, time, and resources.

Plus Grade 3 live event arenas have a minimum weight limit - so youd be restricted in the types of event you can compete at. This is to stop main heavyweights flipping you through the roof.

All in all, the difficulty in making a middleweight is the same realistically as building a heavyweight - only its likely to be a lot less effective and limiting in terms of design.

If you want a pure starter class, the recommendation you will hear nearly every roboteer say every time is to start small - Featherweights, Beetleweights, Antweights, ect. A featherweight is 13.6kg, and you can make 2 of them for the same cost as a middleweight. You then have a large pool of championships and events to attend in order to build up experience to attempt a heavyweight.