First, I've been a model railroader and general railfan for most of my 38 years. I took a bit of a break from modeling myself during my 20s on account of wife / career / etc, but during the whole time I was working on other layouts. I dug back in with a passion about four years ago, ripped out the abortive start of a layout from a decade prior, and started construction of a new layout. I'm an N scaler myself, but most of the other layouts I work on or operate on are HO or O.
Model Railroader is good for beginners. Also be sure to check out Model Railroad Hobbyist, which is a free (er, advertiser-funded) online model railroad magazine. It's aimed a bit more at experienced modelers, but there's still lots of layout tours and the like in there that will be of interest and inspiration. Besides, the price is right to try it out.
One thing you'll start to figure out fairly quickly is what interests you and what doesn't, and that will start to steer you towards certain things. Some of us are interested in exactly replicating some prototype area and railroad down to the most minute detail, whereas some are more interested in just running trains through fantastic scenery that is purely a work of imagination. There are segments of the hobby who enjoy scenery, others that are fascinated with equipment or structure modeling, some that like to create accurate operating practices, and some that really like control systems.
My starting recommendations would be:
- Just get something running so that you can start figuring out what you like and what you don't, with the full anticipation that it'll be temporary. If you start too big of a project on your first try, you'll lose interest before you get enough of the pieces together to make it run smoothly.
- Go find a local show and see what others are doing
- Talk to your relative and learn from him, particularly if he's a relative you like. (And, well, skip this if he's equivalent to my weird uncle Gary.)
If you're interested in the controls side, there's a decent DIY electronics community within the hobby. Two Yahoo email groups I'd recommend are mrrelectronics (general MRR electronics) and Arduini (focused on Arduinos in model railroading). There's Digitrax's Loconet, CMRI, the NMRA's new LCC standard, and a couple dozen other ways to connect a layout to the computer. Then there's things like JMRI, which you've already found, which are great for linking everything together.