Some good advice higher in this thread already. My (okay, more than) two cents :
-If you want to listen to CD's to get familiar with earlier styles, I'd stay away from Lindberg, or other modern soloists for that matter. Don't get me wrong, I'm not saying they don't sound good. I absolutely love Trudel's Trombone Concerti CD, and Jorgen's sackbut CD was the very reason I started playing sackbut. They are amazing musicians who can make any kind of trombone sound good and there's many reasons to listen to those CDs, but I'd argue that learning the style isn't one of them. There are people that spend a lifetime learning early music, reading treatise, reflecting on historical and musicological issues, refining the world's knowledge and comprehension of historical styles...It's a good idea to look there instead, for stylistic inspiration. Couple suggestions : Fede e Amor
by Ensemble La Fontaine with Catherine Motuz and Simen van Mechelen on sackbuts and the amazing countertenor Alex Potter (www.youtube.com/watch?v=IWse2wgIlTk
); the numerous CDs by Caecilia Consort with Adam Woolf on sackbut; also Adam's solo album Songs Without Words
); and if you dig a bit, you'll find more or less historical recordings of the ''classical'' concertos with period ensembles. Ensemble-wise, plenty to find, if only on YouTube. Oltremontano, Concerto Palatino, His Majesty's.......a great album by íSacabuche!...and many others
-Regarding your instrument question... With the type of ensemble you're talking about, you're basically inventing something anyway, so it doesn't really matter what horn you play, whether it's your modern alto or a small bore tenor or a hackbut or a real sackbut... Just play what you feel like playing and what will allow you to express yourself best. And if you'd like to try to play on a sackbut for that, whether it's a good authentic one or a vaguely sackbut-ish horn like the Wessex, by all means go for it. You wouldn't be the first nor the last to use a sackbut in a non-early music or non-historical band.
-The advantage of buying something more ''serious'' than a Wessex is that the day you choose to try going deeper into earlier styles, you're already equipped. But I understand price is a big issue if you don't intend to do that or know for sure. However I'll just mention that your price estimate is inflated. I mean, the best alto sackbut out there is arguably by Egger and the standard model is about 3800 US (quite expensive, but not ''a lot more than four thousand'' - and the two I've played are both among the very best trombones (of any kind) I've ever had in my hands). Noah Gladstone sells the Leuchter alto $2550. I haven't tried the alto, but I tried a few of the tenors, and I agree with the oft-repeated assessment - it's about 70% of the sound for 70% of the price. Personally if I was going to spend that kind of money I'd put in the extra cash and get that 30% more, but that's me. Graham Nicholson here in The Hague is an outstanding early brass instrument makers - he's regarded by many as the best natural trumpet maker out there. I'm pretty sure his price for a trombone would be closer to Leuchter than to Egger - but he's got a fairly long waiting list.
-I can't vouch for the Wessex, haven't tried them. I've tried quite a few very bad sackbuts made by far more reputable ''sackbut'' makers, so I'd be cautious....but in the end with the price of the Wessex, it's not that huge a risk.
-If you do go for a Wessex (or if you somehow find a good used sackbut somewhere for a reasonable price - it's rare but it does happens!), I encourage you to at least try a real sackbut mouthpiece and see how it feels and sounds - it is strange and not super comfortable at first but if you stick to it, you get used to it faster than you'd think and it's extremely rewarding musically. It really allows you to do things with your instrument that your would never be able to do on a modern mouthpiece.
I probably will end up trying to use a very wide rim (which I know is a cardinal sin)
By the way, what do you mean by that? Sackbut mouthpieces typically have very wide rims, by modern standards.
-Been said before, but I'll repeat nonetheless - Get a copy of Adam Woolf's Sackbut Solutions
. Every trombone player should own a copy of that book even if they don't plan on playing historical instruments or music. No kidding.
-You mentioned lessons. I don't know if he still stops by Colorado sometimes, but if he does or if you're ever in the Bay Area, you should get in touch with Greg Ingles. He's pretty much the top American sackbut player, as far as I know. Also, Linda Pearse is a great Canadian bass sackbut player and teacher - she teaches at IU in Bloomington.