On weight, that's simple, N scale is .5 oz + 1.5 oz per inch of car length.
Now as far as trucks and couplers, yes, MT makes all sorts of trucks and you can usually find them at your LHS or mail-order dealer for about $3.50 to $5.00 a set including couplers. Go to their web site to find what you need.
This is correct information, as far as the NMRA recommenations. There is a school of thought that differs. Let me start by saying that my layout is not to the point where I can pass judgement on these ideas, so just take them for what they are.
That's written from the HO perspective, but I think the relevant points are the same. The author really questions adding weight as a method to improve running, saying that it is really just covering up the real problem.