Let's see, first off great choice! I have an overland(OL) myself and I love it. The downside is that sooner or later your main gear will strip so you should replace it with a GPM Titanium Main Gear or the Delrin Main Gear. How fast the stock main gear would strip depends on how you'll run it, if you'll just be doing small 2in jumps and just cruising around your driveway then you'll be fine for awhile. If you'll be trying to crawl over your bed or some rocks chances are your main gear will strip faster. Also it is advised that you don't do wheelies until you get your Titanium/Delrin Main gear

Second to brake would be the front steering knuckles, although I haven't broken mine yet, I would suggest you buy yourself Alloy Front Steering Knuckles because you may break yours from crawling. IMO the stock steering knuckles are durable, they survived my worst crashes from about 3ft high jumps.
Torque, yup, the OLs got a lot of that! Just stick in a 9t or 10t on your motor for you crawling just to be on the safe side as the 11t or 12t may fry your electronics due to "stress" from climbing. The only way I could compare its torque is to a stock xmod(Which I would hate to compare both of these to), so let's just say the OL can beat an xmod in both torque and speed.
The controller is comfortable. Nice, a bit big, but that's good because it's more stable when you're holding it. Requires 8 AA batteries but you can just buy regular alkalines as the controller doesn't drain them fast. Also buy yourself some decent rechargable AAA batteries for your OL. The xmods battery kit works fine. But most people buy Energizer rechargeables or the new Rayovac IC3s w/ 15 Minute Recharger.
Outside equals joy to the OL. You can see how stable it is when driving it on the street(Just make sure your street isn't too crowed

). Stock tires are great! You can buy wider wheels and tires for more stablity and also choose how much grip you want(From most grippy to least: 30g,40g,50g).
You can purchase an OL at ebay(That's where I bought mine), Rcmart/Dinball.com(Cheap prices but since they're from Hong Kong shipping will be a little expensive bringing the total price to about the same from the US), Towerhobbies.com, MiniZRacer.com, HobbyOnSale.com and MiniZStore.com(Also a great place for buying replacement/accessories for your OL). There are probably more places to buy an OL from but those are the ones that come off the top of my head.
Also since you said you want to do some crawling most OLs will get stuck from time to time so you might want to buy some Swamper Tires and a Lift Kit. For more information about those two products you can go over to MiniZRacer.com, click on the forums, then head on over to the Overland section. There's a great abundance of OL crawlers there that can help you with what setup you can use and if you can get a hold of them, you can buy Swamper Tires and Lift Kits from them. There are also some other ways to lift you OL, just search the forum there and you'll see a bunch of different homemade methods by other users. Hope this helps and good luck!