If it all seems like too much, just get your provisional Category D entitlement added to your licence. Then do your bus modules 1a, 1b, and 2. Only then think about modules 3 and 4. That way, it doesn’t seem like too much. And modules 1a, 1b, and 2 aren’t expensive. If you book your module 3 (ie. the practical driving test) with PSTT, they sometimes do special deals where they include module 4 for no extra charge. Best to speak to them though about that, as I could be wrong.