My OP is about implementing the board, Superdat. Just that.
OK so are you saying you know how to do the technical stuff?
You haven't mentioned the type of LED you plan to use? 1W LEDs can be individually placed and a pcb isn't needed but it will need a lot of power.
You could design and make your own pcb, it's not all that difficult. You would need to learn how to use a PCB layout SW, I use a free version of Diptrace.
You are limited to 300 pins but the max size is about a page. If you want to try this method let me know and I'll check the exact size it can make.
30cm is big though, if you used toner transfer you might need 2xA4 or whatever size paper you have in Argentina.
Don't try to make your traces too small 1.5mm max. Alignment of double sided is quite difficult, I didn't find it as easy as is suggested on Utube.
If you do try double sided, make your Vias big so that a little misalignment is OK, otherwise use wire instead.
I did find a method but only after about 4-6 failures.
30cm Sq would be expensive if made commercially.
Do you have a suitable laser printer?
The quality isn't bad but not as good as "made" pcbs.
Light sensitive copper clad is supposed to be better but more expensive (I've not used it). You still need a printer but an ink jet is OK.
If it's a one off as in I'm never going to make another pcb, you could buy a small amount or copper dissolving chemical and sponge the copper until it's gone. No tank.
I don't like ferric cloride, it's a bit too agressive for my liking. I use ammonium persulphate which is a little slower but doesn't try to attack every bit of iron in the room!