SDR or "Standard Dimension Ratio" is a method of pressure rating piping. The SDR is the ratio of pipe diameter to wall thickness. An SDR 35 means that the outside diameter of the pipe is 35 times the wall thickness. A pipe with a high SDR # (thin wall compared to the pipe diameter) has a low-pressure rating and a pipe with a low SDR # (thick wall compared to the pipe diameter) has a high-pressure rating.

The SDR 35 has a very thin wall and will be flexible which is a good thing for sewer gravity drains but not something you want in your dam. As pipe goes I would not use this no matter the fitting type.

As for the fittings. All gasket joint piping should have thrust restraints to prevent movement. If these are done right they can be costly. Depending on the elevation difference in your siphon the velocities when siphon is activated can be quite high. The glued joints are more rigid and that is what you want.

I would use SCH 40 solid PVC with solvent weld joints.
As for time before glue sets up. You have a few seconds to get it together. If you apply glue and put that section together before moving to the next section you should have plenty of time. And the great thing about it, if you do mess up just cut the joint out and start over.

Like Gully Washer said you should determine the drainage area and size the siphon and secondary spillway accordingly.