This is me

Personally, I am working on a few games- a war game, a dungeon crawler board game (like a real old-school board game), and a card game (or maybe a few).
The war game took a month of thinking and a couple weeks of tweaking.
The dungeon crawler is still mostly in my head and a notebook as I try to find the components I need...for free.
The card game(s) keeps morphing into other card games.

I think working on a few games at one time is good. I find that I think of something that doesn't fit in one but fits in another.

Playtesting- I am fortunate to live near a popular game shop that is really big, with lots of tables and every day has multiple events going on. So it is relatively easy to find players, as long as you play something with them as well. I am also fortunate enough to live in a city that is EXTREMELY tech-centric, which allows access to some very bright minds that love to help.

Unfortunately (or not), I do elder care 24 hrs a day, so it gets hard to get to the shop regularly, and I also can't be gone too long. But the employees have taken a liking to me and will talk me through ideas I have if I only have a few minutes to spare.

I used to flit from one game design to the next, having maybe a dozen different games at various stages of development simultaneously on my mind. But now I've selected a "big three" to focus my attention on at once. I'm doing this because I've noticed a tendency to simply bounce from one half-baked game idea to the next, not finishing one game design completely. The result is that nothing I came up with could be considered "finished."

As a hobbyist, this isn't so bad, since I'm enjoying myself immensely whenever I do it. I can even come up with a short dice-based game or Dworak deck in the space of an hour or two. But if I want to be published, then I ought to follow-through with my designs until they're ready to be seen by publishers. This means a complete rulebook, presentable graphic design, and maybe even a sell-sheet for game events/conventions.

"You choose your own level of involvement," it seems. And if you want to see one of your games in the marketplace one day, you owe it to yourself to guide at least one of your projects through to the end.

For playtesters, you could try Meetup or a similar social type service. There are a bunch of Meetup board game groups in my area.
To get students you may want to make it sound good and offer something, if you can.
"rip my game apart to make your game better...plus you'll get a beer during the playtest."

Also, I start with mechanics, theme, or name, whatever comes first.
For the dungeon crawler, theme came first- fantasy, but would work the same in future deep space, or as a good conquering evil, or the other way around. The war game was mechanics; I set out to make a quick, easy to learn, easy to remember, minimal piece, war game.

Another thing I like to do is go to Youtube and find a game someone came up with, then figure out how to streamline it, or change components, or something. The latest one on my mind is a Slenderman game I saw a video of.

The war game was originally designed to create an open-source ruleset that could be played anywhere using almost anything as pieces. With it being that way, my vision for it is kind of opposite of how most companies go about things. I want it to be a complete game at a low price point, with no add-ons. My vision is to include 6 themed factions to choose from & a puzzle piece type of board so you can choose the size when you play.
I am slowly working on my third rev prototype, and I may approach a publisher sometime.

The dungeon crawler is more what I see a publisher wanting. I see it as a 'grand' game, maybe $100 retail. I am torn between fantasy & space, and am developing it to use a double sided board with board pieces that can be used on both sides, and put out by a company that is already established in fantasy & space (like GW), with creatures that bridge the two genres. It is unlike anything I have seen. I have searched & looked at over 100 games 'like' it, but none are it, nor do they play the same way.
Essentially it is players vs DM, with DM having hard, fast rules to play by (like an AI), and the players able to co-op or solo, or both, and also make hard choices that can really change how the game plays out & who 'wins'.

I am a big fan of simple, and really want it to be simple enough that the rules can be printed inside the cover like older classic games.

My goal for it is to have a game that can be setup in a minute & can be played in 30 mins or 2 hours, depending on how players want to play that time.