My plan is to start a budget travel planning business for those who don't want to be in a managed tour. What would you want me to take care of ?

First off, you have to find out who would be willing to pay for this. All the information you describe here is already out there online, if you have the knowledge and the time to research it.

In my view, your segments should be found with people, who are too busy to build a schedule themselves, or don't know where to go and need inspiration on that. But is there a business case in building an audience, that would pay for that service? Traditionally travel agents get commissions from airlines and hotels, that they book with - would private customers be willing to pay for you? "Off-line-travel-agents" already exist.

I could see a business case for an "online-travel-agent", if you would make the bookings also. But that comes with a different responsibility as you would be closer to working as an actual tour operator, and handle when hotels have overbookes, flights cancelled, etc.

What you could consider doing could be building your own niche - trips to Spain, Greece, California, Northern Thailand, South Africa, whereever - and you become THE expert on that area. You would know everything - all sites, attractive accomodation, flights, means of transport, dangers and annoyances - and you build an online universe around that, but also do the bookings. Then you would get commissions from the different operators you would work with and be the source of knowledge about that.

Good luck with your business idea! If you would like to discuss this further, let's set up a call.

Best regards
Kenneth Wolstrup

Here are my thoughts in no particular order:

Travel planning can be very stressful especially with all the endless options of places to visit. If you can save people time and take stress out, you are definitely on to something. As humans we tend to gravitate towards convenience all the time.
Have you experienced what you are recommending? People want to know if you have experienced these places, sites, accommodations that you are recommending in your itinerary.
I’d would also include: packing list, travel apps list, travel podcasts list, emergency contacts.
Can you introduce your travelers to locals? This is huge! People want to connect with the locals during their travels and if you can find a way to make this happen, they will love you forever.
Is this targeted towards Millennials?
Including flight prices is great, but remember that they fluctuate all the time. What about including a list of sites that provide great flight deals?
Travel is a communal activity. Can you introduce travelers to locals or travelers with other travelers?

Does this make sense?

Happy to jump on a call for any follow up questions.

Always with gratitude,

-Cesar