Sit-in (decked) kayaks tend to be lighter for a given length and help protect you a little better from the elements (sun/cold/hot). Sit on top (SOT) kayaks tend to be a little heavier but are becoming ever so popular among the kayak fishing crowd due to the raised casting position sitting in one places you. Due to this popularity, the latter is developing a huge aftermarket for attachments/accessories directed toward the fisherpersons. SOT place your center of gravity higher off the water and thus tend to be a little less stable (albeit this is rarely an issue for the experienced/trained paddler). SOT are therefore often made wider for a given length than decked kayaks to offset this disadvantage. While it's theoretically possible to perform a kayak roll in a SOT, it requires some mechanism (e.g. thigh straps) to hold the paddler in the boat during the roll. Decked kayaks have varying amounts of below-deck storage, desirable to keep the center of gravity of the load as low as possible. Adding more and more gear to the deck of a SOT worsens the center of gravity issue it already has.
There are always concerns about boat weight, how much is necessary, and how to handle that weight. Longer boats generally weigh more but are also generally more efficient at paddling long distances. For river kayaking, you need to factor in maneuverability and generally, will point to a shorter boat. SOT generally weigh more than decked kayaks. There is also somewhat a tradeoff between weight and durability: you don't want a super light kayak that achieve that by using too little or too flimsy material. Most recreational kayaks are made of very durable rotomolded linear polyethylene. In my opinion, thermoformed plastic kayaks are somewhat less durable. Composite kayaks (fiberglass, Kevlar, carbon fiber) are the lightest (and most expensive) of the bunch, but require significant care to avoid hitting rocks, etc. and prevent chipping and cracking. Unless you want to paddle in really open water or for really long distances, a kayak in the 12'-14' range will probably be the best blend of length/weight/tracking/efficiency/maneuverabilty given your stated venues of lakes/rivers. If you're mostly on big open lakes (Falls/Jordan) and paddling longer distances, err to the long side. If you're mostly on moving water/rivers where maneuvering is the key, err to the shorter side.
There are a variety of car top loading and transportation systems that can help mechanically manage the weight of kayaks but generally speaking a pair of paddlers can help each other greatly in loading most boats car top. Many systems allow the paddler to raise and rest one end of the kayak at a time so that its necessary to only lift half the weight at once. As frequently as weight, paddler height can be a hindrance in loading boats and many paddlers will also think about the actual car they drive when planning their outfit. Look to companies like Thule (thule.com), Yakima (yakima.com) or Malone Auto Racks (maloneautoracks.com) for a variety of options.
You'll find a variety of kayaks (particularly decked) that are designed to consider different body sizes. For many small-framed women (or men) a kayak with very tall gunwales or a very high deck can make them either have to reach excessively over the gunwale to paddle or or be "swallowed" in the boat by a high deck and/or too wide outfitting. A great example of this is the Wilderness Systems Tsunami 120 versus their 125 model. The 120 is designed with a slightly narrower beam (width) and deck height as compared to the 125 model. My wife and I enjoy this pair as the perfect fit for our two body sizes.
Inflatable kayaks are popular among paddlers with limited storage or transportation options. The marketplace is flooded with cheaply made options, though, and I'd suggest great caution to buy a good quality one if this is the route you take. Remember that you get what you pay for and a good inflatable will end up costing as more or more than a good hard shell boat. Brands like NRS or Aire are name I'd look for. I'd personally stay away from big-box stores for a major purchase like this. Work with local outfitters (like Get:Outdoors in Greensboro or Great Outdoor Provision Company) in Raleigh to be able to talk with salespeople who know their stuff and who will be around for support in the future. Also, look at top brands of collapsible, skin-on-frame kayaks like Folboat or Feathercraft. I've been very impressed with how well modern versions of these boats paddle and similarly solve the space and transportation problems that inflatable kayaks do. The Oru folding kayak seems all the rage these days and it's an interesting concept but I'd wait a could of years to see how durable they end up being.
All the above being said, let me also point you to one of the best places to learn about all the above and to surround yourself with people with the same interests and questions. The Carolina Kayak Club (
Home - Carolina Kayak Club). This is a well established group with all levels of paddlers that caters to what your needs seem to be. They can answer your questions and in many cases arrange to let you try out or see much of the equipment you're interested in. You'll probably never find paddlers without some opinions they're willing to share.
(Me? I'm an American Canoe Association certified flat water, whitewater and coastal kayaking instructor trainer, tandem canoe instructor and river safety & rescue instructor who currently owns 7 kayaks I paddle personally. I've been teaching kayaking in the Triangle area and much of the southeast US for 9 years and paddling for the last 16 years)