.......... it makes me realize that selling myself would be a full-time job, especially to start, which is hard to combine with my current full-time job. That's especially challenging when I might have to work for free or very cheap initially to get my name out there.
Oh well, I guess nobody said it would be easy........
Marketing. Yup, it's necessary.
NEVER EVER WORK CHEAP. Once you start cheap, clients expect cheap, you're done before you start.
Free work to build a portfolio is another matter. But, for product work, there's no reason to go begging to potentially paying clients to work for them for free or cheap.
Instead, hit up friends, relatives, co-workers with offers of free, pro quality photos of their eBay items. Tell them in advance that you will be working the shoot in a totally professional manner so they won't be expecting a quicky cell phone shoot, then do it.
A few freebee eBay shoots should give you enough product variety to build a portfolio you can show on a tablet or laptop, then go sell yourself and services.
Haha! I've spent a lot of time figuring out ways to create interesting backgrounds and artificial bokeh. Even though white backgrounds are appropriate for some uses (like catalogs), I think they're overused and boring. So I try to make my pictures more interesting by putting objects in a more interesting context.......
The examples you've posted above are absolutely stunning, compelling, beautiful; technically and artistically brilliant.
Now comes the 'But'.....
But, the artistry you are clearly capable of isn't really what a commercial buyer is looking for, methinks.
It's catalogs, advertising and packaging where your photos should be aimed, that means dull, boring, white backgrounds or backgrounds/settings directly relevant to the product's use(s) and/or applications, or settings intended to create the illusion
of elegance, glamor, style, image, hipness, sexy, sporty or whatever. See car ads for example, most all push at least one of those illusions, yet there's nothing sexy or glamorous about a car in traffic, driving a sports car in a sporty manner is often hazardous and dumb.
Your second watch photo above of the Fossil watch looks to me like a good product photo, the gears in the setting make everything relevant. Your first and third watch photos, not so much, the third appears too manipulated.
The clock photo would be fine if aimed at Steam Punks, not sure if it would be a better sell of the clock or the goggles though. Not trying to say Steam Punks aren't a market, they likely are, and quite possibly a very interesting niche to work. .