Hmm, you know, I'm not sure we have a walkthrough on that. Plenty of information spread out over the forums, but that doesn't exactly make it very accessible.
Mostly, you'd want to unpack the contents of sheets.vol and leave the contents in the Outpost2 folder. Loose files will override the contents of the VOL file. Edit the lose files. Don't worry about trying to repack them.
Sounds like you already have unpacking handled, but just in case: There are console mode programs to extract from the VOL files. Namely,
OP2Archive. If you don't want to muck around with downloading and running console mode programs, you can find the contents of Sheets.vol posted in various threads on the forums. They are all similarly named, and posted together at about the same time. For example, the vehicle info can be found in
Reference: Outpost 2 Vehicles - vehicles.txt.
The formatting of the text files is not always easy to read. Fields are separated by a single tab. Depending on the width of text, it may bump a column to the next tab stop and offset the visual formatting. I've heard using a spreadsheet program can help line up the columns. You'd want to save as text though to preserve the original format of single tab spacing.
As there are many columns, the headers as well as the values may both wrap in text mode. Additionally, the headers may be split over multiple lines. That can make the headers a bit confusing looking. It also makes it hard to match the data up to the headers. If you're using a text editor, it may help to disable line wrapping.
For vehicle speed, check the "Move Points" column ("Move" in the first line, "Points" in the second line). Right after it is "Turn" "Rate". Then "Common" "Ore Cost", followed by "Rare Ore" "Cost", followed by "Build" "Time". It's not easy to read in a text editor. There is also a "Production" "Rate", used by build/repair units such as the ConVec, Earthworker, Repair Vehicle, Bulldozer, and Spider. This is not to be confused with the "Build Time" needed to produce vehicles.
To help match up the two header lines, the first entry with two lines is "Track Type" "W/T/L/M" (Wheeled, Tracked, Legged, Miner?). The next column is "Owner" "P/E/B" (Plymouth, Eden, Both).
Hopefully that's enough to get started.