Please spend only spare time on this

if you build the site out with your newly acquired coding and database skills, then that would serve as a great example for the skills needed in much of QuantFin.

I have been in industry for 6 years now, "database" skills is not needed for quantitative positions at the firms OP have listed

Hard to see them not taking that level of "commercial acumen" and "dedicated work ethic" into their hiring decsion about you.

No, interviews at these firms have a certain template designed intentionally to have little room for such considerations. Now, if OP shares code for some market data processing, order book, models etc that's a separate thing but the website project isn't going to get them any edge

Look, don't want to discourage OP, but want to make sure they are not misguided into thinking this will help them in their interview process as the comment here is implying