I would do it this way:
1) With regards to the Deca (well myself I wouldn't use it at all, but in terms of what athletes I've written cycles for have liked and done well with) I would limit its use to no more than 400 mg/week, which most can tolerate, and limit its use to the first 4 weeks because it takes so long to clear.
Some are bothered by anything at or over about 200 mg/week but that is fairly unusual.
2) On the Dianabol, I'm sure there's nothing magic about the number 50, but 50 mg/day, preferably as 10 mg five times per day, is very well-proven.
There is very little issue with regards to increasing adverse side effects with combining the two above drugs except that both aromatize, and so a given person that might get away with either of these alone at these doses without a SERM (Clomid or Nolvadex) or aromatase inhibitor (letrozole or Arimidex/anastrozole) they might well not get away with combining both of these without using such drugs to counter this effect.
3) On testosterone, more gives more results, but if no ancillary drugs are taken to correct aromatization and DHT-conversion side effects, for a fairly novice user about 750 mg/week is a reasonable place to draw the line, as more than that will tend to be much more obvious for side effects.
With regards to combining with the above drugs, estrogen is even more of an issue. I wouldn't combine T with either of the above at these doses, let alone all 3, without dealing with the estrogen issue.
On the DHT issue, dutasteride does a great job. It isn't expensive, and isn't hard to get from overseas pharmacies.
If taking care of estrogen and DHT issues then one can run more T than the above if desired.
On cycle length: Everybody wants it NOW or in the next few weeks. But it's much better judgment to plan in terms of what will get me better results at the one year point from now, the two year point from now, etc.
So for using the same total amount of drugs and being "on" the same number of weeks per year -- and you've got to make such things equal in comparisons for the comparisons to mean anything -- let's compare doing 12 week cycles to doing 8 week cycles.
With the 8 week cycles you can do for example January-February, May-June, and Sep-Oct as your "on" months.
This will get better results than what you're limited to with the 12 week cycles, in which you could do for example Jan-Feb-March, and Jul-Aug-Sep as your "on" months.
1) The earlier weeks of a cycle give more results than the ones at the tail end of a long cycle.
2) Recovery is faster from the 8 week cycles.
Another reason to do it this way is that recovery issues, if proper PCT is used, are almost always about zero with 8 week cycles but very often are issues even despite PCT with cycles as long as say 12 weeks.
Lastly, I would not "taper" the cycle. Of course you will see so many that do it that way and assume they did better on account of it, but for sure there is no need with an 8 week cycle, for sure the actual result is more weeks of suppression, and for sure the taper is a dosage that is unnecessarily weak if you are going to be suppressed that week anyway.
Better to be fully "on" and gaining as fast as possible, or fully "off" and recovering natural T rapidly and pretty seamlessly than to be in limbo for unneeded extra weeks.