I have cranked these motors from a deep cycle trolling motor battery and it worked OK. When I've tried jumper cables directly to the starter, It's tough to get the cable clamps to get a good, conductive bite on the starter terminal and a good ground, especially with the motor vibrating as the starter cranks the motor. On a battery, the jumper cable clamps dig into the lead terminals for more contact area.
The filter bowl has a metal bracket under it - the finger-nut at the bottom of that bracket unscrews and backs down to the bottom of the bracket so the bracket can be swung away. The bowl then may be stuck to the gasket and that is sometimes a challenge. I've gently nudged them with a rubber mallet, but be careful, that can break the glass. I've heard of guys using heat, but I'm leery to try that because an open flame near gasoline. If you break the bowl, new ones are still available, but they run about $35. Some others here probably have tips for getting the bowl unstuck.
I'm thinking your gear oil was recently changed and a yellow gear oil was used. I know Amzoil synthetic gear oil is that color, and I'm sure some others are too. Since it leaked from the top of the gearcase housing with the motor on it's side , either the driveshaft seal is leaking, or the shift rod O-ring. The driveshaft seal is at the top of the lower unit housing, just under the water pump. To get that seal out, you either need a seal puller, or, I get them out by heating the housing around the seal with a propane torch and then wiggleing it loose by prying with a big screwdriver. first you will want to drain the gearoil. The shift rod O-ring is hidden. Below is a link to how to remove it, thanks to Frank for posting this procedure - On your model, the bushing drives out toward the bottom of the housing after removing the lower half with the gears, etc. I have had to use propane heat on the housing sides to do this on some. You will need a new rope seal to reassemble the gear housing halves - just get a seal kit.http://www.franksoutboardtools.com/shif ... mover.html
There should be little or no gap between the compression release valves and the actuator that pushes on them. AS you pull the recoil, watch in the cutout on top of the recoil housing for the compression release linkage cam to follow the channels so the bar gets pulled, If the cam follows the channels properly, so the linkage moves, then it has to be pushing on the relief valves. Adjustment of the linkage is done by loosening the two screws where the two parts come together above the cylinder head and tightening them again while holding the linkage against the valves.
It appears you will learn a lot of new outboard repair skills by the time you are done with this one!