Looking for components needed to route 3 cables on top of toptube for cyclocross bike
If you are going for less maintenance, you may just want to go with full housing. My exposed cables (on my top tube) get water, mud, grime and need to be replaced at the end of each season of cross racing. Extra maintenance during to keep them lubed up.

I would go full housing and use six of these: http://problemsolversbike.com/products/clamp_on_cable_guides

Other things to think about once past the top tube...

Front derailleur routing:

While not the best image (but best I could find of my older CX bike) you can see the routing of the front derailleur will need a cable stop near the top of the seat tube. Mine uses a pulley below the derailleur. You can use the backstop you put in the question.

Clamp on pulley: http://problemsolversbike.com/products/cross_clamps_pulleys

Rear derailleur routing:

Does your frame have stops for the rear derailleur on the seat stay or the chain stay? As the rear derailleur cable comes down the seat stay from the top tube, my cross bike goes to open cable and then back to housed cable for the curl to the derailleur. You'll need something here as well to either route the full cable down the seat stay or more clamp on cable stops.

Rear Brake routing:

If you are using Cantilever brakes (center pull), you will also need a cable stop for the brakes. You can get a seat post mounted clamp or even a seat tube clamp that has the center pull cable stop. Found one here.