Attic Ventilation/Insulation

Home Improvement Experts,
I just moved into an old (circa 1940s) house in Charleston, SC. It needs a lot of work, and I decided to start in the ~1700 sq ft. attic because the house has no attic insulation. I was going to add some soffit vents prior to the cellulose insulation, but then discovered that my soffits aren't connected to the attic. There is a series of 2x4s running the length of the house keeping the soffits separated from the rest of the attic. Now, the attic has two gable vents--the east side has a 2' x 7' triangular one, and the west side has a 2' x 2.5' square one. In addition, there are two turbine vents, one of which needs a strong squirt of WD-40 (it makes an awful noise).
Now, I've run the gauntlet with my question--is this enough ventilation, and have heard a multitude of responses. Some claim it's fine the way it is, others say I need to drill holes through the 2x4, and a man at Lowe's tells me I need to install a ridge vent. However, I'm thinking the guy at Lowe's is trying to sell me something I don't need, because I've read a bunch of times that ridge vents are worthless if you don't have soffit vents.
So, I pose my questions here to the experts and hope I can clear up this mess. Basically, I want to know 1)    If the existing setup is enough ventilation. 2)    If not, what can I do to improve it? 3)    And finally, if I can't afford the improvement, what is most likely to happen (i.e. will the R-values not work the way they should, or is toxic mold going to build up in the house)?
Thanks,
Adrian
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Charleston has a pretty mild climate. What happens when you add insulation is that on cold days, the attic becomes quite a bit colder than it used to be, and moisture which formerly did not get cold enough to condense may now condense in the coldest areas (typically the underside of the roof). Provided that you have enough ventilation to keep the humidity within bounds, you won't get condensation. Also, when you add insulation, you increase attic temperatures in the summer, more of a consideration in Charleston. This impacts on your roofing to some extent.
It would be hard to add soffit vents to your house, and ridge venting is of greatest value in conjunction with soffit vents. You already are ventilating the ridge part of the attic with your gable and turbine vents (WD-40 isn't much of a lubricant, try to use some oil or grease, or maybe replace the turbine). In fact you have a decent amount of vent area, about 12 square feet plus the roof vents. I had a house with a 600 ft^2 attic and only about 2 square feet of gable vent plus two roof vents. I never had condensation problems (Buffalo, NY), Your vent ratio is much better than mine was.
Moisture/mold is only an issue in the winter, and as I said, you don't have a lot of cold weather, so I would not worry about your ventilation. I would, however, consider using faced insulation bats rather than blowing or pouring cellulose. You have no vapor barrier at all, and laying faced bats between the ceiling joists would help to impede moisture getting into the attic (or, at least, into the insulation).

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