A good hand impact tool at almost any price is worth the money. It saves stripping screw heads. Saves tons of aggravation and chasing up new screws and bolts. Harbor freight has a nice one with a large plastic handle that protects your hand if you miss with the hammer. It is on sale now for $5.99, $6.99 flat rate shipping. Maybe slightly more to cross the border.
If you strip the heads, get a 1/4 inch drill bit, drill the heads of the screws slowly. When you get just through the heads they come right off. Leaving the rest of the screw in place. Remove the cover.
Now the screws will usually unscrew with just your fingers, Take those screws to a good hardware store. Get allen head bolts to match for diameter, length and thread pitch.
Get some anti-seize. Put a thin coat of anti-seize on the threads of the new allens. Install with about 5-6 ft/lbs or .7-.9 m-kgs of torque.
The allens look better and don't strip out as easy. If you get leaks replace the gasket, don't just tighten the bolts tighter or you will just have to drill out the striped heads again.
On your sprokets, changing the number of teeth is an easy way to change the way the bike acts. A lower ratio gives you quicker acceleration but cuts top speed. A higher ratio gives you more top speed with less acceleration. Most of us look for a few less rpms at our cruising speed.
I have found the one tooth bigger on the front or two teeth smaller on the rear gives 400-500 less rpms at 55-60 mph.
Any more and the overall performance of the bike suffers.
Leo