Simple answer: your giant spiders aren't really all that much like regular arachnids.
In detail: your basic need is to figure out which features or regular spiders will scale and which ones won't, while preserving the (at least perceived) sportiness.
Exoskeleton: this should scale okay. You might have some features such as legs and joints a little overscaled, as they may need space for actuation. Animals of large scale already possessing exoskeletons are lobster (and other creations), turtles (perhaps this is a stretch, bit the mechanisms could be carried over), and armadillo (again, not strictly an exoskeleton, but an option).
Number of limbs: this should be able to stay. More limbs means each one doesn't need to be as powerful, although your spiders probably won't be breaking land speed records, as the increase in limbs around a comparable space for animals of a similar size means less space for limb operation, and thus a higher number of limb direction reversals over a given distance than a creature with fewer legs.
Cardiopulmonary: give it lungs and a heart like all the other big animals and it'll be just fine. The lungs could work off a relatively fast moving pumping muscle that forces air around the gas exchanges in its abdomen and out through backflow-blocking cartilage somewhere. Or they could be more material, perhaps with a shared wall diaphragm, where one lung contracts while the other expands to maintain constant volume.
Actuation and digestion: this may be more tricky. You could use the fluid pumping method of smaller arachnids, but this would require significant musculature and hydrolics in what will be an already crowded body. Here's the note in digestion: a spider typically emulsified and drinks it's prey. In a large scale, this may not be practical. They'll need a more mamillian digestive tract to extract the amount of energy they need from the amount of prey then y can catch. Big predators like wolves (in packs) or cougar have to for days between meals sometimes. If megarachnid gets all her food from just the available juices, even with acid spit up for some predigestion of solids, it simply won't last long enough between meals to be competitive with other predators.
That said, moving back to actuation , the legs may actually be pretty easy. An exoskeleton gives you a whole lot of room for muscle. And, when you have eight legs, you don't need as much power in each leg. It would probably be just fine by that reasoning to replace the hydraulics with some muscle tissue.
Webs: not specified in the original question, but worth dealing with. Spider webs are made almost entirely of special proteins. So, your spider needs a lot of high energy density food (definitely a predator then). And, while it may seem like that would be a problem on large scale, it may not. Spider silk is close to steel for tensile strength and much tougher on a deformation v. strength curve. It would probably not be inconceivable then for a spider of this magnitude to spin enough silk for low quantity regular use or the occasional net trap or web nest.
Spider appearance: let's see, eight legs, exoskeleton, more than 2 eyes, general scariness—yep, I think you're good!
Edit: to address the pulling capacity: a 30 to 40 pound dog can drag its own weight if the distance is not to great. If this spider has similar musculature spread around eight legs, it could do the same. If it had double the musculature (that is, similar per-leg musculature to the dog), it could be half the size (of said dog, an example of which would be a large Spaniel or a small Labrador or Bulldog).
