No the power steering pump will not fit, not sure where you got that information from. Go to realoem.com and punch in the last 7 digits of your vin for part numbers. As for the driveshaft, use the M3's front section with the ti's rear section, so yes you'll need an M3 guibo. The problem with the diff is that 4cyl BMW's come with small case diffs and 6cyl BMW's use medium case diffs. So you're going to want a medium case LSD, but e36 coupes, sedans and convertible differentials will not fit because they have a totally different mounting system. Since coupes, sedans and verts have multi-link rear suspension and 318ti's have semi trailing arm rear suspension, the rear subframes are completely different. You'll need a medium case diff out of a 6cyl Z3, an e30, an e24 or an e28. If you use an e24 or e28 diff(they have better gear ratios 3.25 & 3.46), you'll need to swap the cover and output flanges with those off of an e30 or Z3 diff. If you want a 3.73 LSD, e30 325is' came with that ratio. Since you'll be upgrading to a medium case diff, you'll need e30 6cyl ABS halfshafts as well since the medium case diff is wider and the stock 318ti halfshafts will be too long.
No worries about the newb questions, just look in the engine swap section of the forum and the differential section, all of your questions have already been answered. Once again, realoem.com is your source for part numbers. You can also use it to do part number cross-referrences to find out which vehicles are compatible. | 
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