Removing the bottom end of an outboard you've not known very long for the first time can be a real pain if it's not been off for a while.
I've always found that patience is the greatest asset you have to resist the temptation to beat the hell out of it, as you'll end up breaking the cav plate.
If its just corrosion between the two mating faces of the castings, and around the stainless dowels that locate between the faces, then hot water will help, so will tapping around the join with a rubber mallet. Note that's sideways onto the join, not trying downwards on the cav plate.
I always leave a couple of bolts in loose as the bottom end can break free suddenly and you may not be ready to catch it.
If the driveshaft splines are corroded into the crankshaft you really are unlucky, the only way I've found to get these out is to try when the engine is right up to operating temperature.
Regardless of how much I've used the boat I always drop the leg every spring to change or check the condition of the impellor. I take the oppertunity to clean and regrease the driveshaft splines, plus clean the mating surfaces of the castings before putting a very fine smear of silicone grease on them before reassembly. Hopefully this will mean I can get them apart in the future.
RIBBED For extra pleasure.
Member of the ebay Blue RIB cover club.
Member of the Bombard 380 Aerotec club