If you go synthetic, like Mobil1 or Redline, you don't need a lighter weight oil, as the synthetics have much lower pour points and cold viscosity than regular oil. I use Delvac1 5-40 year around in Michigan, and have used Mobil1 15-50 as well, with no problem.

On filters, get the Hengst or the Mann. They're both oem, so it doesnt' much matter which one. I just buy whatever's cheapest at the moment. Check Fastlane and http://parts.catalog.mbz.org or some other on-line places. They're cheaper than a local dealer.

You mention the pressure slow to come up. Be sure you replace the little o-rings on the stem that runs through the middle of the filter. They age and get brittle and don't hold the oil in the filter well. Order a bunch when you buy a filter--they're cheap.