Hi Jeff, you'll probably find more help for your questions in other forums here but I'll try to give you a quick start.

ND filters are rated by filter factor, or basically how dark they are. A 2x is one stop and a 4x is two stops. Check out the Singh-Ray variable ND filter which goes up to about 8x or 10x but it's quite expensive. Lots of fun though!

I think you're on the right track with a scanner if you're not going to shoot film anymore (buy it, use it, sell it) but there can be a fairly steep learning curve with scanning. The first few scans might take awhile to get right, but with any amount of automation it should go at least a little faster later. Best results of course would be from negatives or slides (not prints) and if you have slides you might check out a 35mm film scanner with a batch feeder accessory (Nikon has them). Expensive, but a huge time saver and will have a high resale value.

Photoshop is a constant learning process. Check out Scott Kelby's books for a great start (Adobe Photoshop {insert your version here} for Digital Photographers). Also look for the Digital Imaging forum on this site.