It's been about 12 years since I last owned a Pisces, so I'm trying to
remember a little about how the boat was set up.

In mine, the front hatch was a 7.5" VCP, which is easy enough to
replace if it's worn out. My front bulkhead was ABS plastic, as was
the rear. If you have a foam bulkhead, then Minicell is the best way
to go. GOOP will hold it, or you can use 3M 5200, but GOOP is easier
to find.

The rear hatch is held in place with some webbing straps which are
secured to the deck with those D-ring things. Current Designs was
using a similar hatch system on the Solstice series until 2001, and if
you contact them they can probably send replacememt parts. The newer
version is black, not clear, but it's the same part. I don't remember
if they were bolted or pop-riveted in place. If they are bolted, just
unbolt them and remount with the same hardware. If they are
pop-riveted, it's your call. I'd use stainless steel machine screws
and nylocks to remount them.

My seat was molded plastic, but I know the seat you are talking about.
I had something similar in a Skookumchuck, and we'd take the seats out
and use them on the beach instead of sitting on rocks. I'd personally
replace it with something more comfortable, unless you like the feel
of it. The kit kayaks, like CLC and Pygmy would have seats that should
be easy retrofits. Current Designs seats are now part of the cockpit
coaming (either rivited on ABS or molded in), so they would not have a
retrofit. If the Wavesport seat is comfortable, go with that since you
already have it. If it is foam, just bond it in with contact cement,
goop, or whatever is handy.

If you repair the seat brackets, West Systems will be good. There
should be a stop in the seat, where it can slide forward but not back.
When paddling, your feet push back and hold the seat in place. When
not paddling, the bungee keeps the seat from sliding forward and out.

My deck rigging was standard nylon pad eyes, with marine bungee, and
those are easy enough to come across and replace as needed.

Beyond that, there's not much to say about the Pisces. It's far from
the fastest thing on the water, but I had a blast running it through
class II - III- whitewater. She is a forgiving boat.