If you want a good itinerary, just feed your preferences into ChatGPT or use the suggested itinerary in Rick Steves. If you want hotels and flights, given that you have some Spanish, I think you could do that, too, without a lot of trouble.

If don't think you'll save money, though. The one time I used a travel organization (Inside Japan Tours self-guided option), I was very happy with the result, but I do think I paid about a 20% premium over what it would have cost to book everything myself.