The most effective way to collect lots of gossamer is using a sickle on the spider egg nodes that can be found in e.g. the Silkwood or the cliffs south of the big spider near Spinebreaker’s Flank, or in many caves inhabited by spiders.
The easiest way ot get ichor is cooking unappetizing fish. You can get tons of those with just a few fish traps.
I very rarely bother to harvest spiders these days. I just kill them to death and continue whatever I was doing.