you didn't say what kind of back wheel you have, but i'm assuming it has gears and a freewheel, since you mentioned having to take off the rear brake lever.
ideally, you want a thicker gauge spoke and a double wall rim. 12gauge is good, 11 is better (the smaller the number, the thicker the gauge.)
the best you could get are available from Worksman Cycles - Factory Direct Store: America's Oldest Cycle Manufacturer of Industrial Bicycles and Tricycles, Since 1898
. easiest way is to call them up and explain what you need. expect to pay between 100-150 for one wheel.
a cheaper way out is bikepartsusa.com they sell 12g. spoked heavy duty wheels for a lot cheaper, but you'll need to find out what you need first, then search for it, they're not the best at answering questions on the phone, but everything else about them is pretty good.
or, go to the bike store and have them figure it out.
"four stroking" is when your bike sputters along, essentially firing on every other stroke of the piston. this is caused by many things, from lack of fuel, too much oil in the mix, bad spark, too much weight, etc.. don't worry about this yet, your bike's not even running.
as for needing a rear brake? it's true that the front brake does about 80% of the stopping, and if all you ever did was ride in a straight line on dry ground, it's be all you need. but add in a little rain, and a corner, and front brakes are almost useless.
if you brake too hard in a corner with the front brake only, your bike's gonna follow the line of it's momentum instead of turning, and so will you. except you'll both be skidding on the ground. rear brakes are a must for safe riding.