Err, as far I know Eldar are not affected by warp storms since they travel via the webway.
And Eldar living on planets isn't that far fetched, my Craftworlders have settled five planets.
But sending off Craftworlds?
It ain't a kit-car you get in the mail and just assemble.
Well 'modern' Eldar craftworlds, like the big 5, are formed from many dozens (hundreds?) of craftworlds that joined together over time.
Perhaps this planet just has a strong fleet of 'original' craftworlds, which are more like space faring caravans than continents.
Sounds like a good idea. The location of the planet/solar system should be very heavily guarded though, as Eldar do that very well. Especially with something as static as a planet, if orks or chaos or the Imperium found its location, it'd be unable to just slip into the webway to flee.
I'm still developing my craftworld fluff, I'm thinking more of a coalition of smaller craftworlds+colony planets than a huge space faring nation.
Eldar don't really need to physically send out ships for aid though, most of the time they use the webway. In the Fall of Iyandin fluff, Maugan Ra brought an army of Reapers via the webway.
Perhaps your Eldar's planet/solar system is situated in an old 'crossways' of the webway, allowing large scale vessels to quickly reach other craftworlds in times of aid.