Thanks for the responses, I think I can give you some feedback.
My reasons for Zercher Squat:
1) Mobility, shoulderissues make a front Squat position a lot easier
2) Balance, I have long femurs, so a Zercher position gives me better balance and better bar placement without excessive forward lean and good squat depth
3) Safety; I train alone, a Zercher position makes it easy and painless to let the weight on the spotterbars should it be needed, a back squat could be pretty shitty in that respective.
OK that makes sense. Over time your legs will get too strong to be fully stimulated in the Zercher position but for now they seem to be a good option. I'd just suggest working on the shoulder mobility so that in the future you can move to back squats or at the least front squats. I don't know what your shoulder issues are, so this may not apply, but three things that helped me the most were; 1) shoulder dislocations with a band, 2) external shoulder rotation stretches and 3) light weight behind the neck presses.
My reasons for a Rack Pull:
1) Depth, my starting weight was too low, so for proper height I would have needed blocks under the bar or something so I decided on rack pulls to work the lower back. Maybe in time I could switch to deadlifts.
I can understand this. If you aren't pulling at least 135 on the deadlift it can be a hassle to figure out how to adjust for proper depth. I would say getting your body healthy/strong/mobile enough for a back or front squat is more critical to your training than moving to a full deadlift but once you can attain both you will really be in a good position to put on some real strength and muscle.
My reasons for DUP:
Having done things like 2*10 and 3*8 before I like the constant variation better. It also allows me to work the muscles in the entire rep-band which I think is good. I also find the two-week blocks in vanilla HST too limiting at this point. I can progress more this way, adding 5% of my 5RM to all my lifts every workout without paying attention to my maxes. They move along anyway
There is nothing wrong with hitting multiple rep ranges especially if it keeps thing interesting and improves the likelyhood of you adhering to your program. However, rep ranges alone isn't the most critical.
There are two main factors when considering your lifts and it is volume (total reps) and intensity (% of your max). If you do higher volume (lots of reps) you need to decrease your intensity. If the intensity is the same, say 65% of your 1rm there isn't much different between a 2x15 and a 3x10. Granted in the 2x15 you may have to display more endurance within the set that is fairly made up by having to exert similar endurance over the 3 sets of the 3x10. So you want to make sure you are matching intensities appropriate to the rep schemes you are using.
This is why with HST (and many other programs) you start doing higher volume with lower intensities and move to lower volume but with higher intensities. So that you have an accumulation phase (lots of volume) and an intensification phase (lots of intensity). So your rep ranges isn't super critical but your program needs to follow this general idea either on a weekly basis or a cyclical basis. With DUP it is often both weekly and cyclical.
There are other rep/intensity schemes you can use but the next most practical that isn't high volume or high intensity is active recovery or deload. This is where you will do something both less intense and less volume, mainly working on form and creating some blood flow to heal the body.
So putting all these pieces together you can see in the original DUP study a the plan appeared something like this for the first week: 5x8@75% (high volume), 5x1@80% (active recovery), and 3xAMRAP@85% (high intensity). Further as the weeks go by all of the intensities increase but the sets decrease, so that by the end of the cycle you are doing 3x8 and the intensity is closer to 80% of your original 1rm.
Now...all that being said, it is almost non-important if you are a beginner. If you are, simply try and beat your last workout a little bit (1 rep or add 5lbs etc) each workout and you will get some great gains.
My main concern regarding timing still remains, doing all exercices, 10, on the 5's would bring me close to 110 minutes training time wich is too much. So I would drop the arm work, and maybe also the calf raises on that day, since I don't feel much from them on 3*5 or even 4*5?
Regarding arms, They are already plenty stimulated with pulling, pushing and also the Zerchers so maybe I'm not seeing growth because of too much stimulation?
Do you mean 110 minutes is just more time than you have allocated or that you feel its more time than your body can handle. If you just cannot spend 110 minutes then sure cut out the isolation exercises. If you are worried about your body just eat some food during the workout, protein shake, beef jerky, snickers bar etc.
Too much stimulation is a non-issue if you are gaining weight on a monthly basis imo.