Validated there is a market for my idea. Now what?

Unless you have actually found people who are willing to give YOU money; you have not validated the assumption people are willing to give YOU money for YOUR idea (rather, you will have validated the assumption that people are willing to pay for a similar idea brought forward by others).

Don't get me wrong, it's still a great step forward. Next, I would proceed and validate that people are willing to pay you, for your idea. Once you do this, you will right away have your first customers.

Do not start building. Do customer research and customer development. Put up a landing page, drive traffic and start building a mailing list. Start taking pre-orders. Start blogging/writing about your idea. Start appearing on podcasts talking about your idea.

Do lots of customer development... then build an 80% solution quickly and cheaply.

Next you'll want to focus on getting a solution out to them fast that targets only their core problem; don't worry about any bells and whistle features or design.

The real idea here is to get something out fast to get over the "fear of shipping". So many products are sitting half done or half released because someone was to scared to ship something imperfect.

Get it infront of them fast to both get feedback and to ensure you can actually produce.

Well, sounds like you found competition. Can you build a significantly better product than they have? Does your idea have some huge innovative aspect for which their users would just jump over to use your product?

If it doesn't, work on the idea and figure out what you can do better - but don't fall in the trap of adding too many features so you will never finish the project.

After that, build an MVP as simple as you can. Then test it on the market and see if there is interest.

One thing to keep in mind tho. Sometimes an idea is better left in a scratchbook, don't force it if the process above does not yield much merit.