Definitely go to your LBS (local bike shop) for your purchase. A few reasons why:
1. They need your business
2. They know the product
3. They know how to wrench on your bike
4. They will fit you to the bike (very important)
5. They will know what needs to be done to make it work for your needs (racks, trailers, fenders, etc.)
Personally, I'd skip the suspension and just have higher volume tires put on the wheels, they still absorb the small bumps and you'll be less likely to pinch flat, especially with a big load on.
If you buy from a shop, be sure to take the bike back in after a month or so for a tune up, most shops will do this first tune up for free. Reason being, the cables stretch affecting the brakes and shifters, the bearings settle in, and the wheels get out of true.
Since you plan on riding with a load either on or behind your bike, I'd look at disc brakes for sure. They are way better at stopping especially if it's wet and muddy. Think about it, do any of the car manufacturers use drum brakes any more? No, why, discs just work better.
When getting fitted to the bike, the number one thing is comfort. If you're not comfortable, you won't ride, period. The LBS will make sure your bike is fitted with the parts to make you comfy and will swap out the stem, bar and seat either for free or just the difference in price with what's on the bike already (keep in mind this is for a new purchase from them). If you bring in a used bike, they will still swap parts, you just have to pay full price.
Wear a helmet.
If you buy from a private seller, take your new ride in for a full tune up, yeah it will cost some money, but a properly tuned bike is way more fun to ride and it will be safer. Be sure to have all the bearings serviced as well, hubs, bottom bracket, and headset.
Go riding BEFORE you plan to take the bike hunting. Make sure you know how everything works and if it's going to be compatible with how you plan to use the bike. If you ride just 2-3 times a week 3 weeks before you plan on hunting, your butt will get over the saddle soreness. Those big squishy seats won't save you, they just chafe the inside of your thighs, especially when you start to sweat. Be sure to bring a few basic tools and know how to do basic repairs. If you don't know how to remove the wheels, unseat the tire, fix the tube and put it all back together, have the shop show you. Not much worse than walking out several miles with a flatty.
Lastly, have fun! Ride year 'roud, it's a great way to stay in shape! Be safe, shoot straight, and put up some pics of your new toy and some game it hauled out!