1/ Depends on what you mean by "Heavy"
. If you're a PLer & your training triples, doubles & singles for 6 months, then have a time doing a higher rep range, say 8-10, then I'd say fine, but if you mean light, as in easy & not pushing yourself, then no I wouldn't go with light for 6 months unless you want to get weaker.
2/ According to some sstudies (Eric Hultman & Hans Sjorholm 1983) 1.26 seconds & your ATP is derived from Creatine Phosphate degradation & 20% from glycolysis, by 2.52 secs 50% of ATP come sfrom glycolysis, & it takes 6 seconds for maximum contraction to begin to decrease, this is despite the fact that the muscles CP levels are at least 65% basel level, continuing beyond 6 seconds ATP dimishes & acidosis (lactic acid build up) begins to hinder work.
I couldn't find (off hand) the speed of recovery to regenerate CP/ATP levels.
Remember though if you're using sub-maximal weights, you aren't firing all your motor units at once, you are doing reps & building cumulative fatigue, so doing a sub-max set of say 10, will have a different effect than say a double (for a start a trained athlete can tolerate 30% higher lactic acid build-up of an untrained indivdual).
I'd say spending some time on low reps & some on higher made sense for most strength athletes (not 6 months of each, but some), in the sense of staying heavy for the reps reps used, plus the odd time of doing lighter work to give a bit of extra healing time now & again.
3/ As I said I couldn't find the resynth of CP/ATP
4/ You can produce studies for most things. I don't think the negative is the most important part of the move. I think negatives are great, don't get me wrong, but I think concentric moves are just as important. Without practice you aren't going to be able to demonstrate strength either (when do you get asked to show how much you can lower
). I'd say around the 120%ish is a safe amount, but bear in mind that these are very intense moves & the risk of overtraining is bigger than using normal training, as is the chance of injury.
5/ The idea of how long your body is breaking down & building up for is one of those really
contenious things & for every 4 studies you read, you often get four answers, as it depends on what they are looking at as an indicator of breakdown & recovery, Some people do very well on one session a week, but others under train. It may have to do with your maximum potential & how near you are to it, or 101 other factors that could effect recovery rates, but I don't say do not only work out once a week, but nor do I advocate it. The empirical evidence seems to point towards the idea that most people do best doing a 3 day week, looking at the pre-steroid data that's available. Some do better on more, others less, for most people I'd say start with 3 days a weeks, but try less & more periodically & see what works best at that point in your development.
6/ I'd say in the risk stakes the bench is more dangerous than the miltary press (that's in front of the neck), especially if your not careful to balance your back moves, so your rotator cuffs are put in danger (I know that one
). I'd say wide or very narrow grips are as safe as "normal" grip in most cases.
I do have problems myself with anywhere near straight arm flyes (but with elbows, not shoulders).
If I was going for maximum strength I'd prefer cycling up towards a date (say a contest for example), then returning to a higher rep scheme for a while before another cycle up. Some people can mantain near max lifting fine, but my joints aren't fantastic so I'm pretty cautious about when I max out (& in what move). But, I'll be interested to see how you get on working out like this.