New Website Project - Where to begin?

I've been teaching myself programming for a while now and I'm at the point where I want to start a project to put in the portfolio. I got a few books in the mail yesterday; HTML5 and CSS3 All-in-One For Dummies 3rd Edition, The C# Player's Guide (2nd Edition), and Databases DeMYSTiFieD, 2nd Edition. If anyone has any recommendations for additional resources I'm all ears. I'm pretty set on C# as the job I'm shooting for will be using it. At this point I've mostly just done courses on teamtreehouse and codecademy, and I do a lot of HTML emails for work (shoot me in the face plz). I figure the best way for me to really start picking this stuff up is to actually use it instead of just following along with tutorials.

The general idea for this website is to have a mostly automated process for recommending a used price for products (tv's, computer components, electronics in general). The idea behind this came from seeing all of the asshats trying to overprice their used electronics on craigslist, my favorite line "But I paid 1.2k for this back in '05, I'm not selling this 40" HDTV for a penny under $600".

Basically, I want to have a database full of certain products (we'll say TV's for example) with a baseline price, I'm not really sure yet if the baseline price will be static or if I will try to import it automatically from somewhere yet. I guess it would be a relational database (I'll probably be using MySQL), and for the TV example I would have tables for each model number. And then I would have multiple tables relate to that model number with details such as the resolution, the panel type, the year they were manufactured, etc... Then I would take each related table and return some sort of value depending on what is in said table. For example, (let’s say the value range would be 1-10) for resolution, if the tv has a 1080p panel we'll give it a 6, 1440p we'll give it a 7, 4k we'll give it a 9 (by no means am I saying those are accurate representations of the difference between resolutions this is just an example). Once we have values for all of the different variables that would affect the used cost of a tv, we would create some sort of function that places predetermined "weight" on each variable for how it will affect the overall recommended used price. And then we would apply this to the baseline price that is already stored in the database and return a recommended used price. Maybe I'm oversimplifying this but I think it should work in theory?

So my big question is where should I start? Probably not the front end I'm assuming. So do you think it would be better to start just designing and building up the database, or would it be better to just start working on the functions that will draw from the database? Or should I be doing both simultaneously? This is my first go at something like this.

My expectations for this idea aren't high or anything (that's why I'm openly posting it here), it's more or less something to start building up a portfolio and I have no plans of trying to monetize this. So I'm not really worried about someone taking my idea (there's probably someone out there who has already created this anyways).

There is definitely going to be a lot of learning as I go, but if anyone is interested in working on this with me, let me know. The goal is to have a functioning prototype done by the beginning of August and I'll be putting in a majority of my summer into this. If anyone has any recommendations or feedback about anything I'll certainly be appreciative.

We have a similar discussion going on in another thread. Maybe read that at first and then ask further questions related to your projects in this thread.

https://forum.teksyndicate.com/t/database-for-mobile-dev/101153/

Questions are quite similar:

Do you only want to have a website with a database? - Then build an MVC based site.
Or do you want a central API to connect various clients (websites, mobile apps etc.) to your server? - Then go for REST.
Do you have an idea how your database should look like? - start building your backend (database + services or DAOs).
Or do you have a design in mind but no clue how the back-end should look like? - start building a client using mock DTOs.