2-stroke basics: fuel level, ignition, oil ratio, starting

When we took our 16' Larson with 88hp Johnson outboard for a second voyage, we discovered that the fuel gauge showing level is incorrect -- but only after we run out of fuel. Before we ascertained it won't start, we did quite a few attempts. Does it burn the sparks -- and how can I check?
These are all novice questions, with more to follow -- feel free to point out another forum! But any hints are appreciated.

In the process of refueling from a vessel assist ship, while avoiding drift, we put in a mix with too much oil -- 0.5 liters of oil for 5 gallons of gas, 1:20 instead of 1:50.

What would happen after is the engine would go only at high speed. So we just ran around and burned it all. We then got towed by friendly police boat to a slip near a gas station, and put in 4 gallons of thoroughly mixed 1:50 gas. How does it affect the engine, what should we do to "clean" it, if necessary?

Is there a way to verify the fuel level directly in the tank?

What's the right way to start the 2-stroke engine? The guy would warm it up in the morning by giving a little throttle and idling for a few minutes. I wonder, how much throttle should you give the first time on a given day, and how much on subsequent starts? Previous day, it started without any throttling during the day, with just turn-key... Also, should I always check the fuel line is hard before starting?

The way I start is,

-- open throttle half-way down
-- start with the key
-- throttle back and forth a copule times (revving)
-- switch to neutral and go in gear at once

Is it the right way to start? How much "throttling" should I do before going into gear?

When turning the key to start the engine, it makes a short "siren" sound, then 4 lights for engine check turn on and then off one after another. Is this turn-key sound a standard alert?

And to top the day, the key got stuck in the ignition. (Any ideas on getting it out are also useful!)

As you see, we're well into "Boating 101..."

 

Some friends who're into engines tell me, extra oil can blacken the spark plugs, and also soil the cylinder rings. There's supposedly an additive you can use to help with the rings, and spark plugs can be cleaned/adjusted. How likely is it that with extra 300 ml of oil (500 ml instead of 200 ml) these checks are necessary?

 

What vintage is your motor?
Generally the 50:1 oil ratio is appropriate; a bit more oil is sometimes advised if the engine's run full-out all the time. One tank of 20:1 won't hurt it, but don't make a habit of it.
Startup: I take it there's no markings on your throttle box? With the cowling off and the motor NOT running, push the throttle forward. The butterfly in the front of the carb will open (just watch the linkage on the side if the airbox is in the way). You'll find when the lever is around 1/3 of the way forward, the assembly under the flywheel will start to rotate. This point corresponds to the "Start" marking on most throttles. The thing's really not picky, though, and while more throttle is needed for a cold start, none at all can be fine for a warm start. Yes, pump the fuel line bulb before each cold start. (This bulb can also get you home if your fuel pump dies!) My J30 only needs about 30 seconds of idling from cold before you can close the starting pump and put it in gear; generally, as soon as it's running smoothly in neutral at idle, it's good to go.