CD replication and CD duplication are different processes. When discs are replicated, a glass master is made from the master copy that you send to the manufacturer. This is then used to replicate all the discs in the order. This offers the highest quality, but due to the cost of creating a glass master, it's cost-prohibitive for short-run orders. This is the reason that most manufacturers offer only replication for orders of at least 500 units. Duplication is the simple copying of whatever master CD you send in onto a CD-R. This is the more cost-effective process used for short-run orders. No longer considered a poor quality substitute for replicated discs, duplicated CD-Rs have come a long way. One criticism used to be that some CD-Rs had trouble playing in older CD players, but these problems have largely passed, and CD-Rs are often largely indistinguishable from their replicated counterparts.
When deciding on artwork for your CD, a lot depends on the purpose of the project. If it's a CD that will be used as a promo giveaway or as a marketing tool to land gigs, then you'll save money by going for the stripped-down approach. A plain silver CD with the band's name in black ink and a simple one-color envelope sleeve should suffice. Just make sure that your contact info and website address are printed clearly on the sleeve and the CD.
If you're looking to sell copies of your CD, then you need to spend a little more time and money on the artwork. Short-run CD manufacturers offer many printing options, just as they do with large replication orders, so for a more retail-ready look, you might want to at least consider a four-panel insert in a clear jewel case. Even if you pay a little extra for four-color printing on the disc and have the CDs shrink-wrapped, you'll at least have a professional-looking product that your fans will feel better about paying for. It might also be worth paying for the services of a graphic artist to help you with the artwork. Art specifications for the printing process are very specific, so if you're not experienced with graphic design tools, you may run into costly delays.
If you're planning to sell your CD, you really need to have it professionally mastered. A customer will probably not notice whether your CD is replicated or duplicated, but they will notice shoddy sound quality. Mastering will ensure that the levels of all tracks are consistent, the fade-outs and spaces between tracks are smooth and natural sounding and the overall sound of the CD sparkles with a professional sheen and polish. In short, it should make your CD sound like a cohesive work rather than a haphazard collection of tracks.
Knowing how many CDs to order is difficult. It requires that you be realistic about your chances of selling them. If you're an act that regularly plays live shows, then you'll have more opportunities to move product than if you're purely a recording artist looking to sell through Internet stores or from your own website. In this case, it's best to order in small quantities of, say, 25 or 50 and then reorder as you sell them. You'll pay more per unit than you would if you were ordering hundreds of CDs, but saving money on duplication costs doesn't help you if the majority of them are sitting unsold in a box in your garage.
CD manufacturing is a competitive business, and there are deals to be had. It's very easy to get competitive Internet quotes from different manufacturers to see where the best deals are. Make sure that you check the small print to see what features are included in the price and which ones require an extra charge. Some have extra charges for PDF proofs of your CD artwork; others don't. Likewise, some manufacturers include shipping charges in their price quote, while others charge extra. This can make a considerable difference in price, especially if your order is fairly large. Be sure to get an itemized quote in writing so that you can see exactly what is included in the price before you make the decision.
If you're willing to sacrifice a little flexibility in packaging options, there are fully automated digital manufacturers that let you upload all artwork, packaging and content online, where it's kept in a single digital file. Whenever you require CDs in any quantity, you order online, and the CDs are assembled and shipped within minutes. There are barely any labor and warehousing costs, so the prices are very low. (See the Kunaki link below for an example.)