Yes, potentially. There might be reverse current protection on the board, but I’m not sure. Check first.
also, if you plan to run the unit at 18v you’ll need to connect the batteries in series.
My pedals are even cheaper - I (mostly) build them for about £10 a pop!
Admittedly I've just spent 3 times that on my Lovetone Meatball clone, but that's something special!!!
A touch of compression before the octaver, and roll the tone on the bass back a little - less harmonic information into your octaver means it’ll find it easier to find the right pitch.
Valve preamps are a great halfway house between all tube and all solid state (or class D for that matter), my favourite of all being the Ampeg SVP PRO. I've also used mic preamps (TL Ivory 5051) and digital units (Zoom etc) straight into a power amp with good results.
Once you decide to go modular the world of options really opens up.