First, a dumb question (I know, there are no stupid questions, only
stupid people): What is a cuddy cabin?

Rudimentary accommodations under the foredeck.

I'd like to spend under 10,000 TOTAL -- including registration,
insurance, fuel, launching, etc. Which means that the practical limit
is around 8K for a used boat, with 1K to outfit it with "stuff" -- life
vests, cheap skis, etc. Or a 3K boat and a season at the marina.

Oh oh. High on the list of the most expensive things you could possibly buy
would be a cheap used boat. If you spend $8k for a used boat, allow more than
$2k for insurance, fuel, launching, etc. I'd start by allowing $2k for repairs
alone, and hope that careful shopping kept the total needed down to that level.
(But that's just me.)

I live near Lake Michigan, so I am thinking Deep V or modified Deep V
for a hull type. I expect to take up to seven passengers (including me)
skiing, and a smaller number on overnight coastal trips. That means a
practical minimum of about 18'

Seven people overnighting on an 18-footer?
You should not be encouraged to believe this would be desirable or practical.

I think. My tow vehicle (Durango) is
limited to 4500 lbs, so that limits me to 23' max. I want it to be
seaworthy (i.e., safe), can pull novice skiiers and tubers, and --
ideally -- be capable of cruising 70 miles across Lake Michigan to
Chicago.

35 miles offshore with 7 people aboard?

You need a bigger boat. You need to spend more money. Or, you need to scale
back your ambitions a bit.



I'm not interested in Bayliner. OK I'm interested, but I know better.
Sea Ray and Chris Craft seem to be popular brands I know.

"Brand shopping" is much less important on a used boat than new. Especially if
you're dedicated to the $8k price range, you are going to be looking at some
very old boats. Get the boat that's in the best condition among the options you
can find, not the one that was originally sold under the most prestigious brand
name.

How should I do this?

Reexamine your priorities, ambitions, expectations, and budget to start with.
There are a few mismatches in the mix.

Third, what is the value of these online boating classes?

You can learn about the rules of the road, basic safety equipment, basic chart
work, elementary first aid, etc. You can even pass a test that says you're a
"boater" and maybe get a discount on insurance.
In some of the organizations that administer these tests, you can go on to be
an "instructor" without ever setting foot on a boat. I'd recommend the on-line
course, or a basic boating course conducted by the USCG Aux or the Power
Squadron, but remember when you're finished that you're still a "beginner" (as
are we all, to one degree or another). You will learn more in the first two or
three days you are out in your boat than you will in 2-3 months of
class......but that should not be interpreted as an opinion that the class work
isn't valuable.