Here's what I picked up when reviewing HVLP systems for CWW's Feb/Mar issue:
1. I think sanding's been covered here. Fresh coats of lacquers & shellac will burn into the previous layers so the only reason to sand would be to get rid of dust or runs/sags. Basically, follow the manufacturer's instructions.
2.The Fuji system performed very well, excellent fit & finish, but I would upgrade to the Q series. The standard model really is quite loud. Not terrible, but I'd seriously consider hearing protection if I were going to be using it for a long time. I think the Q is probably worth the money.
3. The Fuji's swivel side fitting for their gravity cup is really nice – it means you can almost always have the cup in an upright position even when spraying at weird angles, such as when doing a cabinet interior.
This becomes moot, however, if you get the 3M PPS conversion. This replaces the standard pressure cup with a molded plastic one that holds a heavy-duty "baggie," complete with a filter, that contain the finish. (Italrowe has posted a link (above) to the system at Wood Essence's web site.) The cup is pressurized which compresses the baggie and forces the finish out through the gun. With this setup you can spray at any angle, including upside down. Cleanup is a snap: you can either store finish in the baggie/cup for a short period, or rinse out the baggie for re-use. The cup stays clean.
4. I'd suggest you get a whip if one is offered. The lighter weight & better flexibility make a huge difference. The extra length also means the pressurized air is a bit cooler when it reaches the gun. This can be an issue with shellacs & lacquers, not so much with WB.
5. A starting package will depend quite a bit on what you'll be spraying and how often you'll use the system. For applying "finish/stain to wood" you'll want a 1.2/1.3mm needle with matching cup. You could probably go as small as a 1.0mm if you watch your viscosity and thin as necessary. For paint you'll want to go to at least a 2.0mm needle/nozzle set and if it's gooey stuff like latex you'll almost certainly have to thin with water and a retarder such as DynaFlo, Floetrol or Target Coatings' SA5. The spray unit's instructions should have a table for use with a viscosity cup. Basically you time how long it takes the finish to flow through the cup & then dilute as required so it'll spray.
My subjective observations after using the units are covered in the CWW article so I won't repeat all that here. Have a look at it. With any of the units a bit of practice is in order. Get some cardboard to spray onto and get a feel for how the unit works. Increase & decrease the amount of fluid, then play with the air pressure. See what combination works best with various viscosities. Also adjust the fan pattern of the spray; doing this also changes the volume of finish being sprayed, so it will probably also require adjusting the air pressure. (I know that this isn't very helpful pre-purchase. You can't just walk into a supplier's store and start spraying paint all over the place.)
If you're considering going the route of using a HVLP gun with a standard compressor, don't think you're going to get adequate performance out of a 6-gal. Porter-Cable pancake. (I've tried. It sucks as much as it sprays.) You'll need lots of air volume and a good air filter in your line. It's a nice feature of using the turbine units that they provide clean, warm air to the gun.
A note re Rusty's comment about airless: If you have a house to paint, go airless. Airless is what professional crews use when they paint acreage such as aircraft hangars and factories. They lay down a ton of paint, fast. HVLP on the other hand, is slow like tortoise. Does a great job but takes quite a while to get it done. Also you need to use caution. Airless is EXTREMELY high pressure.
As for the units reviewed, all worked fine. The Wagner is great for painting fences & outdoor furniture; does a super job for the price. The Earlex 5500 was the real sleeper. It looks sort of gimmicky but it performed on a level very close to the more expensive units. It does a better-than-adequate job for a very reasonable price. The Fuji Mini-Mite has all the control you'll need to spray almost any finish. Fit & finish are very good. I'd upgrade to the "Q" version as it's a bit loud. Here you'll have to ask yourself, "Am I going to spray enough to justify spending $250 more for the Fuji instead of the Earlex?" Both are good; the Fuji's more versatile and that could be a game winner at some point down the road.
Edmonton-based Lemmer has three models, with 2-, 3- and 4-stage turbines, the difference being that with more power you can spray faster or spray thicker coatings. This is a professional system with excellent fit & finish. The T55Q (2-stage) system is less expensive than the Fuji MM. The Lemmer turbine is QUIET. (I bought the Lemmer T90Q and the extremely low noise was a deciding factor in the purchase. The T75Q & T90Q both have models with turbine speed controls which makes them even quieter.) Lemmer uses the 3M PPS system and also includes a small 250-ml paint cup for detail work where a larger cup would be awkward.
Apollo Sprayers are the Rolls-Royces of the HVLP systems targeted at the home buyer. They have all the bells & whistles – variable speed on some models, automatic speed control, LED pressure indicator, LED warnings for filter blockage, etc. The finish on all parts is impeccable and the "feel" of the gun was probably the best of any tested. Excellent customer support. If you've got deep pockets, give these folks a call.
But the guys in Edmonton are worth a call . . . www.lemmer.com . . . if you're feeling a bit nationalistic