I ended up putting a 3/4" plywood gusset on the top and each end of the truss with about 15-20 nails. glued along with the mending plates and just a mending plate on the other side. I think it is enough the wind is strong enough the snow will not likely be on the roof long. Looking at the suntuf documentation the want a 2x purlin so I will add that. I do not intend to hang anything from the bottom chords.
Yes, your trusses will work just fine, especially now that you added the glued gussets to them. They're probably overkill, depending on snow load you might see. I didn't need to, but I put gussets on both sides. That just makes sure I mitigate any flexing effects on the joints. 9 feet isn't a long span in the grand scheme of things, but that bottom chord will eliminate any outward force on your walls. Nails or screws for assembly doesn't matter, other than keeping the truss flat in its plane while handling it. I.E., don't let it flex side to side. But you shouldn't have much trouble with those considering how small and light they are.
Not sure why you would need a 2x purlin on a roof that small and with trusses on 16" centers, but if that's what the manufacturer wants, you should probably heed that. I used 2x purlins as well, but laid them down rather than standing them on edge. If I had it to do again, I would double the number of purlins I used instead of just putting the minimum recommended by the roofing manufacturer. Your roofing manufacturer may have a minimum fastener penetration in their design. In the event of a severe windstorm, the plastic sheeting is going to tear away before a purlin fails, which might actually be a good thing (to prevent complete destruction), except for anyone downwind of you (flying plastic debris). Just make sure to follow all the instructions for the fasteners. Usually on stuff like that polycarbonate roofing, there's additional or larger washers required to prevent it from tearing out easily.
That's gonna be a very strong roof, structurally. Don't doubt your design. It will likely hold up anything your walls will support. Your trusses will tie the walls together and make the whole structure very rigid, especially with the bottom chord going all the way to the ends of the top cord. If you're putting sheathing on the walls, that's when you'll really notice it getting rigid. Believe it or not, that's still triangles at play. Sheathing prevents the structure from racking and twisting, as well as makes vinyl siding installation much easier.
Short soffits and eaves will do a good job of mitigating lateral wind drag that normally lifts a roof. The hurricane ties will certainly add to that protection. I would still recommend a vent on the ridge if you're not going to put any climate control on it. Obviously you're not putting a ceiling in it, otherwise there would be no point in translucent roofing. A ridge vent will equalize any pressure in the event of a tornado or high wind to prevent implosion or certainly blowing out any windows you put in it.
Is this going to be a growing/planting shed, or are you just using the translucent roofing for daytime lighting? A small solar system would be a great addition if you need lighting.
I'll point out again, if you want 5 ONLY
ways to build a truss, just ask 5 experts. I'm not trying to be an expert, just lending my design and experience. I tend to put a lot of overkill in what I do to make something strong. What I do might cost more than what someone else might do. It's just what I think I want at the moment, whether necessary or not. I used to build doll houses for the girls in the family, and I'd build the roofs strong enough for me to stand my 200 pounds on. Simply because I know what kids will do when you're not looking. I didn't want the roof to cave in and hurt the kids if they decide to climb on them. Overkill? Certainly for a doll house, but not for the kids' safety.