You might find some useful information here: http://www.thetandemlink.com/tandems.html
1. Frame Material: Frame material alone will not necessarily yield a "stiff" tandem, at least one that's stiff in the right directions. Some lower-cost aluminum frames are, for example, not as laterially stiff as some of the better air-hardeneded cromoly frames. With respect to your team weight, you're about average for most couples who buy tandems. Any of the more recognizable tandem-speciality builders will produce a tandem that would be stiff enough for recreational rides or touring. Traditionally, Cannondale's frames (aluminum) tend to be the stiffest, next are Co-Motion's tandems (Alum & Chromoly), and then Santana (all models), all by design. However, they're each a bit different in how they approach stiffness. Cannondale's tandems are uniformly stiff in all directions, whereas Santana makes its tandems stiff to resist twisting but a bit more compliant with respect to vertical flex for added comfort, and Co-Motion is somewhere in between but decidedly more stiff. Mind you, these are all academic characteristics since tire and wheel selection, along with each team's riding style and expectations for what they think is too stiff or not stiff enough and that's why test rides are SO important.
2. Budget: It's all about the money. If you only have $1,500 to spend you'll be hard pressed to find a new tandem from one of the major tandem-specialty brands that offer entry level tandems, e.g., Santana, Co-Motion, Burley, Trek, Cannondale, and Bilenky. Thus, your options are to buy a economy model from one of the other major producers like KHS, Raleigh, Schwinn, or Fuji or a used model from one of the aforementioned builders. The economy models and used tandems will allow you to decide if you enjoy tandeming and serve you well unless you're predisposed to prefer the higher grade or latest and greatest components. Personally, I think second hand tandems from the tandem specialty dealers are the best values (newer than the mid-90's) since they will in almost all cases have a better frame than even the newest mass producer's tandem. By better, stiffer in the right dimensions. Bottom Line: What you usually get when you buy a Santana, Co-Motion, or Burley is most likely a dealer who knows tandems a bit better than the guy who can sell you a tandem. It is the value that tandem speciality dealers add, as well as the very personalize customer support you get from the small business tandem specialty builders like Santana and Co-Motion that justify the added expense but you have to take advantage of their services to get that value. In other words, a tandem specialty dealer will take the time to teach you how to ride your tandem and will usually be able to offer you test rides on several different brands or models of tandems. When you have a question as to why something does or doesn't work the way you'd like on your tandem or want to know if a certain component is compatible or will work better, when you call the small business tandem speciality producer like Santana and Co-Motion you can actually talk to the company owner or, in their occasional absense, the general manager or the folks who designed and spec'd the components for your tandem.
3. Wheels: Like 1/2 bikes, the key to good wheels are good components, the skills of the wheelbuilder, and the wheel builder's attention to detail. Most of the wheels that come on the speciality tandem models are hand-built wheels using pretty good components and the ones that come of the tandems are usually spec'd for all-around use. For extensive touring use where wheel weight and aeo drag aren't major drivers, you can't beat a 48h wheel built with a tandem specific hub and something like a Sun Rhynolite rim laced four or five cross. They tend to be strong, handle lots of weight without breaking a sweat, and also make for a very plush and comfortable ride even on a very stiff tandem.
4. Lessons: The best way to learn how to ride a tandem is to buy it from a tandem specialty dealer, even it it involves a short day trip to get there. The better dealers will take the time to take you and your stoker out for an introduction ride separately, teach you how to mount, start, stop, and dismount the tandem, and then make sure you as captain have gotten the basics nailed down before putting your stoker on the bike so that your first experience together on the tandem is successful... which can be the difference between a life-long love of tandeming or one or two rides with a stoker who never gets comfortable and who ultimate says, no thanks. That said, there are some well-written articles that do a very good job of describing the tandem riding technique linked off of the Web page that I suggested to you at the top of this page. There is also a short video that was produced by a member of the Tandem@Hobbes list that makes attempts to illustrate the starting / stopping method. They caught some of the basics but missed a few others, such as the captain swinging his leg over the front of the handlebars ala track-bike rider style... a good way of making sure you never accidentally kick your stoker or nick up your top tube with your cleats as you mount and dismount.
This is a link to the posting from Tom -- who is a newbie tandem rider -- that introduced his 1st attempt at the Video clip and you'll find a URL that takes you to the video there: http://search.bikelist.org/getmsg.as...10507.0368.eml
These were my observations on the video: http://search.bikelist.org/getmsg.as...10507.0373.eml
P.S. Maybe I need to compile all of my postings over the years into a manuscript?