how to sand back this timber?

All this beautiful old timber (300 x 35mm) came out of a pergola that was taken down in a recent reno (there's another 10 planks where that came from - all 3-5m long!), and I'm thinking of biscuit joining it all up to make a desktop for the study.
I'm happy for it to be a little 'rustic' - don't want a mirror flat surface and happy to have a few gaps for charm, but I need a new sander and wondering whether to invest in a random-orbital or a belt sander? Which would be more effective to clean up this lot?

On another note (not so important), does anyone know what timber this is? I was thinking jarrah but not 100% sure. Any ideas?

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