I have played a few Stretching Metamorphs over the years. In my experience, how the other players reacted towards me was based more on my character concept than the stretching power. My last Stretching character, "Goth", was a person that could transform into a Shoggoth. None of the other players acted as if this character were comical to them.
In terms of character builds, Stretching is the 'other' way to use STR at Range (TK being the alternative). As such, most of my Stretching builds leaned into this and were Quick Bricks.
I typically would have 1/2 Campaign Maximum STR (so I didn't step on the toes of true Bricks) and supplemented my damage with a Multipower that included a HA and a HKA (for automatons or inanimate objects, the Special Effect would be changing your hands in sharp or spiked objects).
I didn't find the need for a VPP on most of my Stretching builds unless the character was also Shape Shifting Metamorph.
As Stretching is essentially Ranged for STR, powers that use your STR, like Clinging and Extra Limbs (a Special Effect for a Stretching character could be to have long arms that can loop around multiple foes), are efficient utility powers.
For defenses, just about any Defense Power (or even the Combat Luck Talent) are appropriate.
For a Movement Power, I typically use Leaping with the Special Effect that I stretch to a location and pull myself there.
In regards to having One Thing, one of my favorite Stretching characters, "Tar-Pit", had a Campaign Maximum AP Clinging Damage Shield.
As Hugh suggested, the Ultimate Metamorph for 5E is a good resource for ideas. I hope this helps.
Doc Samson got a reaction from Derek Hiemforth in Stretching Sourcebook?
Doc Samson got a reaction from Pariah in A DC Animated-style HeroMachine
