Beginner-level macro - flash setups?

With my new DSLR, I want to do some beginner macro stuff, mostly with adapted SLR lenses, tubes, for the fun of it.

The DSLR (Lumix G85) has on-board flash, but I will need side lighting and such.
I have a number of legacy flash units, small and a potato masher, which I assume could be used as slaves.

I am not sure what a system I could rig on a budget.
Skip the legacy stuff?

It would be nice if I could use it with SLRs as well.

Notes:
I am aware of older flash units high voltages.
It seems like the legacy traditional PC connector has disappeared, Huh?

It would take 2 adaptors, Yashica Dental Eye with ring flash, Yashica C/Y to Micro 2/3rd adaptor then a single post post flash adaptor that matched the pins on your G85. The Ring flash can be taken off (I think) and used on other lens as well. Problem of course is that it unlikely that you can get adaptor to use the Dental Eye on a DSLR. If you shoot then any cheap Yashica body will work just fine.

Living in the desert I shoot macro outdoors year long, don't need to use a flash.

An optical slave can be used if you want to trigger a legacy flash using the light from a camera's built in flash.
You will need to use manual exposure and shield or modify the light from the built in flash.

An optical slave with some gaffers tape and the cameras on camera flash is a great cheap trigger that will keep the camera isolated from the flash circuitry. A radio trigger is better, but it's an investment. Strobes can be helpful avoiding long exposures and associated difficulties with macro but my experience, which was with lf black and white film, I needed a lot of strobe power. I needed a big studio pack strobe, I had a hard time getting exposures I could work with using a potato masher. Working with small format and digitally you'll get lots more milage than I did with smaller strobes, and it's absolutely worth experimenting with. But I find it's a lot easier to use continuous lighting and deal with long exposures in macro work. It'll, of course vary based on your exact equipment, what ratios you're trying to get to, subject matter, and what you're looking for aesthetically. Good luck, it's a lot of fun

The Lomo ring flash works, but it does need a socket to plug into although there is an activation button on it as well.

Close up example with Lomo ring flash.

What and where are you shooting? Back when I did a lot of product photography, and was first starting off, I mostly just used cheap, garage shop-lights and white poster board (and sometimes silvered car front window shades) as reflectors. It worked really well. The lights were halogens, so they got hot pretty quickly, which could be an issue. You might could try using LED lights, which weren't an option back then. Since they're a constant light source (instead of a flash), it's a lot easier to set up the lights on small objects to control specular highlights and shadows, which is pretty important. It also makes metering a breeze. Later on, I was given a ring light and acquired some speed lights, but I still used the shop lights for macro type stuff until I got some professional studio lights with modeling light capabilities.

Now, if you're shooting outside or on location (away from a power outlet), or shooting something that can't stand the heat (bugs, some delicate plants, or animals), that probably won't work for you. But if you're looking for the cheapest way to get the best results, that might be it.