Hello and welcome,
ad 1)
Ptpar([0, w, 0.5, x]).play;
ad 2)
e.g.
...
\lag, Pstutter(4, Pseries(0, 0.05)),
\midinote,Pseq([[72,69,64,60],[72,69,64,59],[72,69,62,57],[71,64,62,59]],inf),
...
Obviously here Pstutter’s repetition number is based on the fixed loop length. A dynamic loop length would require a slight adaption, i.e. coupling of those params.
ad 3)
Essentially Pseg should do what you want, e.g.
...
\lag, Pstutter(4, Pseg(Pseq([0, 10], inf), Pseq([60, 10], inf))),
...
For a jump back e.g.
...
\lag, Pstutter(4, Pseg(Pseq([0, 10], inf), Pseq([60, 0], inf))),
...