If you're racing in the power events (sprint/kilo/team sprint) these pedals are great. For everyone else, they last forever but are a bit overkill. The choice between single and double toestraps is more one of comfort than security. Modern laminated toe straps basically hold you really well insofar as they don't break and don't stretch, but you have to strap your foot in pretty tight so you don't lift your cleat off the pedal and come loose. For some people a single strap just creates a pressure point that becomes very uncomfortable, and a double strap is more comfortable. The double strap helps secure the forefront of the foot a bit better, but with 7400's and the matching cleat that's largely irrelevant because the cleats lock into the pedals and don't allow any forefoot motion.
As far as lacing double straps goes, you choose the way that puts the straps where they hold your feet the best and don't create pressure points on your foot. The three basic methods are:
1. The rear strap goes through the loops like a single strap would, and the front strap simply goes under the front of the pedal, wraps around the foot, and goes over the top of the toe clip. For small feet this is often the best approach, or if you have bigger feet and like to keep your cleats fairly back on your foot.
2. As illustrated above, the front strap goes through the loops like a single strap would, and the rear strap goes into one hole on the back plate, out the other hole, then wraps around your foot. Typically the front strap goes over the toe clip and the rear strap goes through the toe clip loop, but occasionally people do it differently.
3. In a variation of #2 and usually a bit better, run the front strap into the outside of the pedal (just like for a single strap) but pull it out through the inside hole on the back plate, up around the shoe, and through the toe clip loop. The rear strap goes under the foot behind the pedal, goes into the outside hole on the backplate and through the strap slot on the inside of the pedal, and then up and over the toe clip.
#3 is a little neater and keeps the straps from bearing at an angle on your foot as much.
It helps in any of these cases to connect the two straps somewhere up on top. Kashimax double straps come with a square patch with four slots (two for each strap) but you can make a nicer one with a scrap of nice thick leather from a cobbler and a little work with an exacto knife. These are more to manage strap pressure on the top of your foot than to position the straps.
Remember that on the track you basically strap in and stay that way, and you have the time to get your feet into the pedals and strapped down. If you are considering this setup on the road, you simply can't tighten up and unstrap enough with double straps every time you stop for a light. For that kind of application, this is poseur behavior. Frankly on the road, clipless pedals with cleats are really the nicest. If you don't want to use cleats, then use a classic frame pedal like the various MKS models, because you can't get 7400 toe clips any longer and the pedals are outrageously expensive.
The SPD-R's are a nice alternative and easy to set up with a single or double strap, but they have the problem that not many shoes are still available with SPD-R drilling -- and you can't mount the cleats without the proper drilling. And SPD-R pedals are getting really expensive as well. I use them and love them, but you have to hunt for shoes, custom modify the pedals, and sometimes have to look for cleats and pedals. At least they are bulletproof so once you find a pair you'll never have to find another. They look ugly with scratches from the cleats right away but nothing stops them from working well.