Overheating by the sound of it. Maybe blocked water intake, blocked water passages, failed thermostat or, ultimately, a failed pump. Try cleaning the intake and water passages first, before you do anything else - that's favourite.

That motor has both an overheat and a low oil pressure alarm, your lack of output from the telltale indicates the former.

First, make sure your battery is fully charged, and that all electrical connections to the battery, solenoid, and starter are clean and tight. If all connections are OK, and the starter drive gear still does not rise to the flyywheel when the starter is energized, you either have a starter that is failing and not turning at a high enough rpm to engage the starter drive, or a worn starter drive (most likely). Try lubricating the starter pinion shaft with a light spray of penetrating oil- if the starter will now engage the flywheel, this is a sure sign of a worn starter drive gear. If you have a 2 stroke 50hp you can replace the starter drive gear and spring, and remember to clean the pinion shaft, but do not lubricate it when installing the new parts. If your outboard is a 4 stroke, you will have to replace the starter, as the drive gear is not available as a replacement part.

Fit a front hitch and do it backwards, or unload the back end if you can. Or use a winch. Driving up a steep ramp, the weight is going to be moved towards the back of the vehicle.

But unless you have a steep launch ramp and a boat right at the edge of the rated tow weight, it may just work no problem.

No. the screw cap on the top of the magneto cover is for timing purposes- the cap is removed to time the engine, and then replaced to seal the magneto components from possible exposure to water. Don't put any oil in there!