I think a similar structure can be used for other sports. Certainly the principles, albeit with different exercises, are applicable.
The role of the GPP will depend on the level of the athlete, but in general it is to prepare the athlete for the specific work to come in the SPP and Comp phases. Whether this means an athlete needs to build his general fitness, hypertrophy, tendon strength, or other capacities will depend on the athlete.
Some of the work in the GPP can continue into the SPP. Tempo will capacity continue to improve; Jumps and Weights will continue to increase in intensity; Medball throws will often continue, but perhaps in lower doses; long hills sometimes are included on Saturdays; and of course speed work is pervasive in all phases. The key of course is progression.
The 3/1 schedule, I believe, is used year round. The exercises and quantities that are unloaded will depend on the plan and goals of the block.
Not sure on #4.
I think Charlie will state that SE in the GPP is inherently not possible because the level of speed required for the given SE is not developed yet. So the GPP for L-S will be longer than S-L, focusing a lot of tempo as well as hills for speed so as to develop the general fitness and initial acceleration required for the first SE runs that will begin in SPP. Some users also prescribe a period of Intensive Tempo to bridge the gap between GPP and SPP and tempo and SE.