if weight is the main parameter, go for it.

Toseek makes a 150gr. CF seat post... CHEAP.. under $25 on Temu...
most of the weight is the clamp. replace the screws with titanium to save more weight.
The ti screws and bolts can also be found in a wide range of sizes and configurations... start with the ones holding the steering stem together and in place.

you'll have to research the cranksets yourself.. WAY too many options there... if you go single speed, the bike will lose a pound or so.
square taper crank? again, the ti fasteners will help, and a ti BB assy will shed even more weight... i find used ones for $50-100 at times. My Marin MBX500 BMX bike wears a Ti BB.

Here are some of the lightest bicycle seats available
Tune Concorde: 73 grams
Tune Komm Vor: 83 grams
AX Lightness Phoenix: 62 grams

no, i didn't check their prices. too early in the day for that sort of shock therapy.

and a light CHAIN can remove another 2 ounces or more.....
from another site..
"I recently weighed 4 chains all broken to 110 links:

Campagnolo Record = 229g (extrapolated 241g per 116l)
Yaban SLA110 = 237g (250g)
SRAM PC-1170 = 239g (252g)
Wippermann 11SX = 251g (265g)"

KMC also makes some super-light chains, and they are, usually, more reasonably priced... My MBX500 wears a lightweight gold colored KMC

a KMC X11EL can be had for about $45, via ebay.

tubeless tires/goop/stems/rim tape/rims add weight, compared to a good lightweight clincher tires, rims, and TPU tubes.

Brifters are HEAVY compared to Downtube shifters, and the DT shifters also require far less cable/housing lengths.