Pre planned trip

I've done a bit of travelling with travel agencies who preplan and book everything for you (accommodation, transport, activities,...) I really like this because while on holiday I don't want to waste time on it.

But this way of travelling became too expensive for me. So I'm looking to preplan my next trip (to Vietnam) myself to save some money.

I think accommodation and flights are pretty easy to book online.

But my question is how do I book the taxi's, night train, activities,...?

Any advice is greatly appreciated I'm really new to this.