sindhu, is.t.i, r.s.i

Three possibly early words of the civilization in India are
semantically related to: ocean, brick and poet. Do these indicate
derivations from PIE or I-Ir? Or, are they all from substrate munda
with some Mesopotamian contacts?

sindhu, 'ocean':

In Yasna 57.29, hen.du, 'ocean' [eastern and western 'hen.du];
us.hen.dauua 'emerging from the river/ocean'.
Thieme links R.gvedic sindhu from *si(n)dh 'to divide'. Can this be
related to sinda 'wood from Meluhha'?

Brick:
is.t.i, is.t.aka, is.t.ika (Vedic)
is'tiia (Avestan)
zCmo-is'tuua 'clay brick' (Avestan)
xis't (North Persian)
is'cem 'clay' (Tocharian)

Poet:

What are the IE etymologies for the words, r.s.i 'seer', kavi 'poet,
singer, smith'?