Tell us about yourself!
I am considering a variation of your circuit to build a helicopter external power source, called Ground Power Unit (GPU). Helicopters work on 28 VDC. I would use two 12 Volt gel batteries and two 2 V cells. Could you be so kind as suggest adaptations on your circuit and program? very many thanks.
Metalworking Tools and Materials
Try the "Toner Transfer Paper" by Pulsar, is great stuff. The blue film is no good.
About etchant: don't spend time trying everything. The best, that is used by the machines and also works great at home, is a 30 to 40% solution of Nitric Acid. It is also easy to dispose, just dissolve it with abundant water and hit the drain. Use a small fan to disperse the irritant fumes.
Right after etching, I spray with Shellac, it will take solder at any time, and it's a great flux.
I find that th easiest way is to use a hot air PVC soldering iron that has no temperature control. You find the best combination of temperature and airflow that will melt and blow away the solder. Piece of cake.