What are the rules/community consensus about participating in your own challenge?
The person that asks the question isn't the one who picks a winner so...
Yes, particpating in your own challenge is allowed, no matter of which challenge type. The Help Center says:
It’s also OK to participate in your own puzzles.
But if you participate in your own challenge, it is recommended to wait some time before posting an answer to give others a chance to participate. Please see: Presolving Golf Questions
If your own answer is actually the best (according to the objective winning criteria) and you want to accept an answer, it's up to you whether you want to accept your own answer or someone else's answer. Personally, I would accept someone else's answer, but that's personal opinion. Also, accepting your own answer doesn't change very much, because if you accept your own answer, it won't be listed higher in the answer, but accepting someone else's answer does.