When building you're own effects you will be soldering a lot so investing a bit more money in a good soldering iron and solder is definitely worth it.

I'm currently using a Miniware TS100 for soldering components. It's really affordable, fully programmable and works really well. You can even flash it with custom firmware. So far I'm really enthusiastic about this little device, heats up quickly and works smoothly. I can recommend getting it together with an extra BC2 tip. Bought mine on Banggood.

For a bit more oomph I acquired a Hakko FX-888D. The Blue with yellow one of course because that is how the original designer conceived it.

For cables and connectors I'm now using the Hakko too. When I need even more power I've got a Velleman VTSI80.

I've tried some solder gauges but ended up with 0.7mm2. I've found 0.5mm2 to be too thin and 1mm2 too thick with the TS100. 1mm2 works well with the Velleman though. I have no experience with lead-free solder, I've only worked with 60/40 Sn-Pb solder. The 0.7mm2 I'm using at the moment is Stannol HS10.