Looks like any generic 12" woofer. Stamped basket, tiny motor, paper cone, and foam surround. They get produced for like $5 each and rebranded when ordered.

Don’t expect much in the way of bass extension or high SPL. Speaking from experience the best usage is 70-300Hz in a 3 way speaker.

A speaker crossover is one of the best choices to learn good soldering. It isn’t difficult if you follow good practice.

1. Use sandpaper to strip back some enamel on your inductor leads.

2. Clean all your leads with isopropyl alcohol before assembly. Dust or oil can degrade joint quality.

3. Grab some 63/37 solder, .6mm thickness is good for most projects. This is ideal for beginners, as it immediately goes from solid to liquid at the correct temperature, and you won’t accidentally add too much solder to your joints.

4. Set your soldering iron to 300C, up to 350 for large joints. Although usually you should try a larger tip before raising the temp.

5. Tin the tip of your soldering iron first, then the tip of each lead.

6. Twist the leads together with pliers. Use some tape or helping hands to hold components in place while soldering.

7. Apply heat to the joint as you gradually feed in solder.

8. If you apply too much solder, use some stranded wire to wick away the excess.

Kits are a good way to start, I would recommend the Hitmaker MT, it is more neutral than most and gives you a good reference point for future builds.

https://www.parts-express.com/Hitmaker-MT-Bookshelf-Speaker-Kit-with-Knock-Down-Cabinet-300-7116?quantity=1

The kit comes with a cabinet so you just need to glue it together.

.25" is too thin, you would need substantial bracing to avoid audible resonance. If you do laser cut a speaker cabinet you will want to bond several layers together.

I would also recommend purchasing a measurement mic. Being able to apply EQ based on your actual in-room frequency response is invaluable.

https://www.minidsp.com/products/acoustic-measurement/umik-1

If you don’t already have a pair of good subwoofers, that would be a strong addition to your setup. Bookshelf speakers cannot really play the bottom two octaves of music properly, and even if they could it isn’t ideal. Room modes limit bass performance, optimal placement for bass quality usually conflicts with optimal positioning for stereo imaging.

For DIY subs, an Ultimax 15" in a 4ft sealed enclosure with a Crown XLS2002 is good value.

https://www.parts-express.com/Knock-Down-MDF-4-cu.-ft.-Subwoofer-Cabinet-with-Blank-Baffle-300-7088?quantity=1

https://www.parts-express.com/Dayton-Audio-UM12-22-12-Ultimax-DVC-Subwoofer-2-ohms-Per-Co-295-512?quantity=1

https://www.crutchfield.com/S-iOpiNYr307W/p_859XLS2002/Crown-XLS-2002.html

The XLS2002 may seem expensive, but it has enough power to drive a pair of subs. If you own a table saw then you can make the cabinets cheaper. Either way you will need a jigsaw or router to cut the driver hole.

It looks like L5 and L4 have the same orientation. I would change one of them, inductors near each other should be on a different planes.

Punch holes in your mounting board and stick the leads of each component through. It is much easier to twist and solder that way, none of the components will interfere.

Also consider moving the tweeter crossover to its own board, so that you can mount it high up in the cabinet. Makes for a cleaner and easier working environment.