Hi,
Sounds like a great project -- a couple thoughts:
200 sqft of collector is a good amount for a 1500 sqft house -- it will definitely make a big dent in your heating bill -- especially given that you live in a good sun area.
I would think about making the collectors vertical. The advantage of this is that they will have much less tendency to overheat in the summer. I pasted in two runs from Radiation On Collector below -- the first shows the radiation on 1sqft of collector tilted at 40 degrees, and the other with the collector vertical. You can see that they both collect about the same amount in the winter, but in the summer, the vertical collector only collects about 1/4 to 1/3 as much as the tilted one -- this is good.
In your climate, an overhang to further reduce the summer gain might be in order. You can design it with overhang tool here:
http://www.builditsolar.com/References/SunChartRS.htm#Overhangs
The other advantage of vertical collectors is that they benefit from ground reflections -- especially if you have snow on the ground.
I think that triple wall polycarbonate is probably overkill -- the dual wall is quite a bit cheaper, and should work fine. Be sure to get the stuff with the UV coating on the outside, and be sure to get Polycarbonate, as it has a very good (270F) temperature capability. I'd think about going with the half inch or thicker stuff -- its easier to handle and work with and needs a bit less support. You may want to think about some way to vent your collectors in the summer. It would be easier on them if they were not exposed to high temps all summer -- this is really true if you go with tilted collectors -- they will just cook in the summer without some kind of venting.
On the collector. There are two kinds of air collector design that I think work well. The thermosyphon design uses the bouyancy of air to move air through the collector -- no fans or controllers needed. These have to be designed carefully in that if flow passages are to tight, you end up with low flow rates, high temperatures, high losses and an inefficient collector. Flow through absorbers work best on these thermosyphon collectors -- the air is introduced at the bottom on the sun side of the absorber, and flows up and back through the absorber and leaves the collector at the top on the back side of the absorber. People have used expanded metal lath (several layers), furnace filter media, and 2 or 3 layers of ordinary black window screen. This is the thermosyphon collector I use for my shop. $350 for 120 sqft, and it works very well -- has a 1 year payback.
http://www.builditsolar.com/Projects/SpaceHeating/solar_barn_project.htm
The article at the link tells you how to size the vents and air passages.
The other air collector design that works well is the backpass, solid metal absorber, fan forced flow. Basically this is a solid metal absorber that has flow passage behind it that is about 1 inch deep that air is cirulated through at the rate of about 2.5 cfm per sqft of collector. The airspace behind the absorber needs to be baffled such that air gets to all parts of the collector. The travel length for the air from inlet to exit should be around 20ft to get adequate heating. The 1 inch and 2.5 cfm are important in that they ensure you get good mixing of the air, and lots of air contact with the absorber.
I just put up a really good book on designing and building this type of collector:
http://www.builditsolar.com/Projects/SpaceHeating/SolAirHtSysBook/SolAirHtingBk.htm
Thanks to the authors, its a free download!
There may be other good collector designs besides these two, but bear in mind that there are a lot more bad designs out there than good ones 
The book also has quite a bit of material on using the crawl space as a way to distribute heat from an air collector. I think that converting your crawl space to a conditioned space is a good thing to do whether you use it in your collection scheme or not. I did this to mine, and have been very happy with the results. I'm not sure you really need to vent it any time of year -- the stuff I have been reading indicates humidity levels in conditioned crawl spaces are lower all year long than form vented spaces, but you might want to do some checking on that.
Using the crawl space to distribute heat might also make sense -- I'd read that part of the book above and see what you think. One advantage of using the crawl space for heat distirbution is that you get some thermal mass from the floor/walls/dirt and that helps to prevent overheating in the afternoon, and provides some heat from the mass in the evening. You could also think about some mix of routing the collector output directly into the house and into the crawl space. This might allow you some control over how fast you get heat in the morning, and not overheating in the afternoon.
Gary
Radiation on Collector runs -- look at the "Total" column
40 degree collector tilt
Month by Month Summary of Sun on Collector
(100% sunny weather)
Collector Area: 1.0 (sqft)
Collector Azimuth: 0.0 (deg) measured from South
Collector Tilt: 40.0 (deg) measured from horiz
Latitude: 40.0 (deg)
Altitude above SL: 0.0 (ft) Above Sea Level
Date ---- Sun ---------------- Collector -----------------------
Month Day Direct Di- Total Direct Difuse Total
Normal fuse
1 21 2192 127 2320 1707 112 1820
2 21 2600 156 2756 2002 137 2139
3 21 2917 207 3124 2147 183 2330
4 21 3095 302 3397 2053 266 2320
5 21 3162 384 3545 1924 339 2263
6 21 3181 426 3607 1849 376 2225
7 21 3061 416 3477 1863 367 2230
8 21 2914 354 3268 1946 313 2259
9 21 2713 252 2966 2009 223 2232
10 21 2429 176 2605 1887 155 2043
11 21 2121 133 2254 1654 118 1772
12 21 1974 113 2087 1532 100 1632
Sum 32359 3046 35404 22574 2690 25264
Radiation in BTU/day
Vertical Collectors:
Month by Month Summary of Sun on Collector
(100% sunny weather)
Collector Area: 1.0 (sqft)
Collector Azimuth: 0.0 (deg) measured from South
Collector Tilt: 90.0 (deg) measured from horiz
Latitude: 40.0 (deg)
Altitude above SL: 0.0 (ft) Above Sea Level
Date ---- Sun ---------------- Collector -----------------------
Month Day Direct Di- Total Direct Difuse Total
Normal fuse
1 21 2192 127 2320 1665 64 1729
2 21 2600 156 2756 1657 78 1735
3 21 2917 207 3124 1380 104 1484
4 21 3095 302 3397 864 151 1015
5 21 3162 384 3545 525 192 717
6 21 3181 426 3607 397 213 610
7 21 3061 416 3477 495 208 704
8 21 2914 354 3268 808 177 985
9 21 2713 252 2966 1277 126 1403
10 21 2429 176 2605 1571 88 1659
11 21 2121 133 2254 1618 67 1685
12 21 1974 113 2087 1586 57 1643
Sum 32359 3046 35404 13843 1523 15366
Radiation in BTU/day
