Welcome to the addiction.
Like almost all things in spey, there seem to be as many philosophies about what equipment setup to start with as there are speycasters. My personal philosophy is to choose the setup with an eye to establishing a solid foundation of technique. A new shooting head is cheap, in the grand scheme of things. You can, and probably will, tweak your lines, leaders, tips, and running lines endlessly to adapt to different fishing conditions and changing personal preferences. But your first few weeks out casting can have a surprisingly long-lasting impact on technique development. So, my advice would be to worry less, right now, about what you're going to fish for, and how, and more about what will help you establish a well-rounded foundation as a speycaster, particularly meaning to:
(1) Build a solid understanding of the fundamentals of the spey cast -- rod loading, anchor, D-loop formation and proper alignment, avoiding errant tip movements.
(2) Recognize and overcome the bad tendencies introduced by single-handed muscle memory.
(3) Become comfortable early on casting off either shoulder.
Most people these days start off with a skagit or scandi head. Aside from being very effective tools for close quarters and winter conditions, the upside of the skagit systems, as has been alluded to, is that they are perhaps the easiest to get to "do something". The flip side of this is that this more forgiving nature also makes it easier to ignore, or indeed develop, certain casting faults. The other downside is that they are something of an extreme case in terms of spey equipment. This goes double for the "switch" or "short" heads (20-ft length). Skagit heads aren't a natural fit for touch-and-go casts, and thus are limiting of horizon in a certain sense. I think there is a lot to be said for starting with a scandi system. Scandi lines are also relatively easy to learn to cast -- not too short, not too long -- and I think offer more rounded practice with both touch-and-go and waterborne-anchor families.
There are tons of line choices, a good shop can help you put something together. My personal choices in that configuration would be:
For a scandi setup, the SA scandi extreme, probably around 480 gr. Airflo
scandi compact in the same weight, also an option. For running line, something in the 30lb range in a contrasting color, e.g. the orange Airflo
30-lb to contrast the Airflo
scandi, or one of the Rio
running lines (I like the blue .035 one, as most of my heads are green or orange) to contrast the orange-bellied SA scandi.
Poly leaders for the scandi head are a good match. A floating leader and maybe one sinking one (pick your sink rate) to get under the surface some is good, IMO.
30-lb dacron backing, whatever color your running line is not (white always works), enough to fill the reel when your thickest line + leader is loaded on. I don't know your reel, put on more than you think you'll need, take off what you don't need. What you need is going to sound like way too much if this is your first spey reel. 250 yds or more is not unheard of on a big reel.
For skagit heads I like the Airflo
compact, good turnover with heavy tips. Add a couple MOW tips, plus tippet, you are good to go. 10-lb maxima covers a lot of bases. You could go for either the medium (T-11) or heavy (T-14) tips in this range. A 5/5 and a 10-ft straight sinking section would be a good start. 10-ft of T-14 is harder to cast, messier, but, turns over big flies better.
It goes without saying that hiring an instructor would be a wise investment. You've got the rest of your life to fish. Getting rid of bad habits takes, at least, ten times as long as acquiring them. Also, the 7/8 weight range is a very popular one, a good instructor may well be able to help your try out some different head systems to find your precise line weight preference.