[BRaWNy]

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

Zig 1
A1) Flat Bench vs A2) Row variation
B1) Neck Press vs B2) Pull Up variation
C1) Floor Skull Crusher vs C2) Preacher Curl

Zag 1
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)

Zig 2
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

Zag 2
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)

PS
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