fantasy draft pick trading for non-keeper

I have a couple questions for all the fantasy football experts and commissioners.

I and the commish of a 10 team PPR league on NFL.com I have tossed around the idea of allowing the trading of individual draft picks prior to our draft. We redraft every year, it's non-keeper, and I am hesitant to change our league to a keeper league since this is our 4th year and we haven't had the same owners in any two or more consecutive seasons. First season was a 10 team, second season was a 12, last year was back to 10 and this year is so far looking to stay 10 and may be the first season we've had the same owners. I'm thinking that adding the ability to trade individual picks will add an interesting aspect to the draft. Obviously it would have to be balanced trading like 1 pick for 1 pick, or 2 for 2, etc. So everyone ends up with 15 picks. Do you think this is a good idea or am I setting myself up (as the commish) for a headache? How would you go about facilitating the trades (ie process of proposing, accepting, and approal/league vote/veto).

The other question I have and I've googled and googled and have come up with little help online as far as setting up a value or point system to ensure draft pick trades are as fair as possible. As in if a team wants to trade up for a first rounder, it may take 2 or 3 good early-to mids for the first and a late pick or two. How do you establish a system to know if a trade is reasonable or not. We'll have a 15 team roster, starting 1 QB, 2 RB, 2 WR, 1 TE, 1 RB/WR/TE flex, 1 Def/st, 1 Kicker. So 9 starters 6 bench making the first 90 picks theoretically the most valuable assuming teams fill their starting spots first and bench last. Perhaps more realistic would be the top 80 are the most valuable since most people draft kicker last or near last. That makes the remaining 70 picks less valuable. How would you set up a value system for each pick? I'm thinking once I have a good point system, then I can set rules like the trade has to to be equal +/- x number of points. if it exceeds that +/- limit it is either void or is up for review.