It's a strength program so it's good for any strength level.
The best reading I've found so far about the 5x5 is
HERE
To be perfectly honest with you, although I'm doing 5x5 right now, HST is the best pure mass building program that I've ever done. Since strength specific training is going to take me closer to my current goals, I'm doing 5x5. However, when the time comes to work on getting bigger instead of just stronger I'll be coming back home to HST with more strength to use on the program.
If your goal is getting stronger with a nice side effect of getting bigger, then 5x5 is good. If it's just to get bigger, stick with HST.
To answer your question about where to start at, I would suggest this, kind of like taking a two week block in HST and subtracting 5 or 10lbs (whatever your progression is) for each workout, you can do almost the same with 5x5.
Just take 8-12 (for 8-12 weeks) increments instead of 6 from your 1RM Do one increment per week. If you are squatting for example 200x1. Then you will start at 120x5 and ramp your sets up to that weight the first workout (heavy day). The next one you will ramp up the same as your first 3 sets from the first one (light day) then the 4th set will be a repeat of the 3rd set. The third workout is a repeat of workout 1.
Next week, you add 5lbs, 10lbs, or whatever your chosen progression is and do it all over again.
Like this:
Squat day 1: 80, 90, 100, 110, 120
Squat day 2: 80, 90, 100, 100
Squat day 3: 80, 90, 100, 110, 120
Next week
Squat day 1: 90, 100, 110, 120, 130
Squat day 2: 90, 100, 110, 110
Squat day 3: 90, 100, 110, 120, 130
You will apply the same method to each of your big lifts (squat, dead, bench, row), that's the ones I use because I can't do the olympic lifts so I replaced them with these.
The accessory lifts like crunches, overhead press, pullup(or lat pull), curls, skull crushers (or tricep pushdowns) are done either 3-4 sets of 4-6 reps or 3-4 sets of 8-10 reps...whatever turns you on.
It sounds a little complicated, but it really isn't that bad once you get into it. Like I said before though, if you just want size stick with HST. If you want strength so HST can make you freakin huge - then do 5x5 occasionally.
About the calves. If you are doing deep ATG olympic style squats and deadlifting, you won't need much direct calf work. Again, it's a strength program, not really bodybuilding (looking like a bodybuilder from it is a nice side effect though), so each muscle isn't directly trained specifically like it would be on a pure bodybuilding program.
