Checking the tightness of hardware is always a good idea.
Correcting the chock linkage so the chock fully opens also should be done. As it is probably an automatic chock, it needs to be checked when running and warmed up.
A dipstick or checking process that results in too high an oil level will lead to oil consumption. Every engine (including small engines with a combined fill plug and dipstick) that I've ever dealt with requires the plug/dipstick to be screwed fully in to check oil level. If you are filling the oil level to the full mark with the plug just resting on the opening, the oil level is being set too high and could well be your problem.
How have you been determining the oil level?
A 30 weight oil (there is no such thing as 30w oil) will be thinner at operating temperature (and burn more easily) than a 10w-40 oil. Stay with the 10w-40 oil.
If you end up replacing the breather valve, you might as well buy a valve cover gasket as well. Before accessing the breather valve, be sure dirt/grunge is cleaned off the area so it doesn't get into the engine.
