Hi Michael,
Yep, Optimas and any other "hybrid" battery types (most maintenance free ones, like Delco Freedom and Die Hard Gold) will require over 14 volts to fully charge. The factory batteries designed for our cars will work with at least 13.6 though, but that's why some people have battery problems when they get a "better" battery and wonder why it's half dead all the time!
As to bulb wattage. The lens pattern is what will make the most difference. Putting high wattage bulbs in a DOT light is a waste. But with a true Euro light, high wattage bulbs WILL put out more light on the road, period. But to use anything over 60 watts WILL require relays. Just don't listen to that drivel from Stu about connecting up high & low beam at the same time - that's dangerous and a great way to blow up your lights. I still recommend looking at PowerBulbs.com for bulb purchases, or contact Dan Stern at lighting.mbz.org.
The 143A alternator is to upgrade the stock 70A unit mostly for a stereo system, but also for the lights. The high-output bulbs with relays will pull 35+ amps on high beam, with the aux driving lights lit. That doesn't leave much for running the rear defrost, blower, electric cooling fans, and other electrical loads. The alternators are available used for $75-$100, but yes, they are $350-$1000 for a rebuilt or new unit. You can find 110-120 pretty easy but the 143-150A ones are more scarce, only used on late models with V8's. It should be a bolt-in with my serpentine belt setup. On your OM617 engines I'm not quite sure what options you have beyond about 70A without some custom fabrication, but if you stick with "normal" bulbs you shouldn't need it anyway!
Regards,