No I don't use 5/4/3/2/1 for Deadlifts, or better, I haven't used it yet.
I find it too much for Deadlifts, to go over 10 reps total in a set.
I do straight sets and sometimes 3/2/1.
I also tried 1/1/1/1/1 Cluster.
I avoid to go to failure in Deadlifts and avoid high reps in a straight set or in a mini set of a Rest-Pause.
I do so in almost every big compound movement, like Deads, Squats and their variations and GMs, because the higher the reps, the higher the fatigue and higher the tendency of the form/technique to be lost.
It's OK to do 5/4/3/2/1 with Deads, well the reps are 15 in total, but you never do more of 5 in a mini-set/part of the set.
I train side delts together with front delts in an upper body day.
But if someone prefers, he can train side delts apart with traps in a lower body day, so that the muscle groups are even apart at the split, and he can use upright rows with a widegrip to hit side delts and traps.
I doesn't matter so much how the split is, it matters which exercises you select for muscle groups.
For example, if I have side delts with upper body, I will not use upright rows, because traps are involved and the movement is similar with movements of the lower body day, like power cleans or power high pulls.
It's a little bit confusing to explain with the splits etc, I try to make my plan with less overlapping and with ways it will fit to me etc.
The base is to use upper/lower split, but there can be some auto-regulations with some muscles and exercises, especially if someone uses 2 choices for every Zig and Zag day (Zig1, Zag1, Zig2, Zag 2).
For Delts I use press movements.
Standing Barbell Press, Standing Behind Neck Press sometimes, Standing Dumbbell Press .
Rarely I do them seated.
I also use the push-press variation at these movements, except behind neck.
Sometimes I do Bradford (Rocky) presses.
The side delts are getting some work from the above movements, but I sometimes include some Lateral Raise variations, or Dumbbell raise and upright rows if I choose to have side delts apart, in a lower body day with traps.
For a better idea, my current/latest split is:
With antagonist alternating sets
A1) Flat Bench vs A2) Row variation
B1) Neck Press vs B2) Pull Up variation
C1) Floor Skull Crusher vs C2) Preacher Curl
A1) Romanian Deadlift (Rack Pull) from a little bit under the knee (midshin) vs A2)Ab Pull Down
B1) GMs vs B2) Front Squat
C)Power Snatch or Clean Drills (sometimes I do them before RDLs, to "wake" up my CNS)
A1) Incline Bench vs A2) Pull Up variation
B1) Lateral Raise variation or push-press variation vs B2) Pullover
C1) Incline Barbell Extension vs C2) Incline Curl
A1) Back Squats vs A2) Incline Reverse Crunch
B1) Hyper or GHR vs B2) Ab exercise
C) Power Shrugs, and sometimes Regular Shrugs extra added
I do my Box Squats either, but I use them lately as part of the warmup sets before Back Squats or Front Squats in a DE manner.
I don' train directly forearms and Calves (my Calves are big enough and get a lot work from some lower body exercises and the power drills, my forearms take a lot work also from the pulling movements.
I am suffering a bit with tennis elbow at my left elbow, just began after my right tennis elbow cured, and it had taken me about a year to go away.
I feel it a bit with Curls, Pull Ups, Lateral raises and a bit lesser with the power movements, but I can handle it)
I don't do any more conventional Deadlifts.
They involve quads also, and for quads I have Front Squats and leg extensions sometimes.
I do Back Squats with a powerlifting style (and I go pretty well full) withe a medium to wide stance, the bar low on the traps and doing them more with the glutes and back and less with the quads.
I don't do olympic "high bar" style Squats, because they don't fit me, as I have long limbed thigs.
So for Deadlifting I prefer Rack Pull Romanians and everything involves more my posterior chain