Stock offset is 25mm I believe.
Don't know about the weight, but they aren't light.
I stole this from another board and can't take credit but I hope it helps:
The things you need to consider when buying new rims are:
1. width- how wide of a tire am I going to eventually want? If the biggest tire you can imagine is 325mm or 13.5" then you can consider 17x9 a good bet. The widest tire you can safely mount on a 17x8 rim is 12.5" or 305mm
2. bolt pattern- 6 on 5.5" or 6 on 139.7mm
3. center bore- just has to be bigger than 47mm for the Titan. Most aftermarket wheels have a bore of 82mm
4. backspacing- to ensure your wheels hit the back bump stop before the tires hit the frame you'll want to find a wheel with 5.5" backspacing OR LESS.
5. front spacing- a 17x8" rim is actually nine inches wide from outside edge to inside edge. (don't ask me why.) So if you select a 17x8" rim with 4.5" of backspacing you will have 4.5" front spacing. This measurement is important if you want to know in advance how the wheel will line up with the edge of the fender. To make sure you get the look that you want jack up the truck, remove one wheel and hang a piece of string (weighted on the end with a nut or washer) from the top of the "wheel arch" and then measure the distance from the string to the wheel mounting surface (where the wheel studs are mounted). If your rims have 4.5" of frontspacing and you measure out 5.5" then your wheel will be recessed into the wheel well one inch.
6. After you've found some wheels that are appropriate for the first five categories you choose what kind of finish and design you want.
Hope that helps.