I started messing around with zinc plating near the end of 2016, there certainly is a lot to read out there on the subject. One important prep step is to soak your parts in 5% white vinegar first to remove any rust or old zinc plating, it won't hurt the steel unless you're really patient or forget they're soaking. After a day or two soaking I'll clean the parts with green scotchbrite or with a wire wheel then again with acetone just before plating. Be sure to spray on some WD-40 if parts will be sitting overnight or longer before plating. There really is no need to resort to products that claim to do a better job for $20/quart...
Whichever plating bath recipe you choose remember to use 5% white vinegar, Kosher salt, distilled water (both don't have any other trace metals or minerals) and my favorite...
Imitation vanilla extract. It's chemical name is Vanillin or something like that, apparently it is used as a 'brightener' which essentially inhibits the growth of large zinc crystals on your parts so they'll look shiny like a paper clip rather than crusty like a galvanized bucket. Getting a smooth, shiny finish isn't as easy as the reading made it seem, but everything will polish up in the end. And if you aren't satisfied, back in the vinegar it goes to strip the zinc off ready to try again.
For polishing I recommend one of the vibratory polishers that people use for cleaning their brass casings before reloading their ammo. Don't mess around with building your own unless you're in it for the adventure. For polishing media, the corn-cob pet bedding works very gently and produces good results. Polishing small parts by hand isn't worth it, bigger parts yes.
For a power source I've been using my regular, plain old, not smart, not automatic, 25-year old, Craftsman battery charger.
I guess they're called Manual Battery Chargers these days.
In my reading I found a few people wiring a bike headlight (or car i suppose) in series with your plating bath, it's there to limit or increase current to your plating bath and you can wire in high/low or both beams depending on your needs.
Try lots of different methods and find one that works for you.
I like de-rusting with plain old 5% white vinegar, or using the electrolytic derusting method with the washing soda and battery charger for heavily rusted or large items.
There is so much you can do with this stuff and if you home-brew it, it's pretty cheap and relatively safe. Just read everything you can find before starting.
Don't worry too much about hydrogen gas production, it's not a large amount and is produced rather slowly anyway.
