Most positive ending for me had them work with the NCR but also have Veronica wither in a library with ideas that would never be used.
Is there another way...? Also, would it be better to remove the elder?

I also know that the new elder will ask me to eliminate the van Graffs, which will be a problem for me as I promised Jackson I wouldn't.
And I think the new elder refuses to help the NCR?

Well if you want to avoid eliminating the Van Graffs stick with the old elder, if you want them to be able to work with the NCR stick with the old elder.
If you want Veronica to be happier your better off convincing her to leave the brotherhood. Frankly I think she'd have been better off heading east to join Elder Lyon's brotherhood.

If anyone is going east, it's benny.

But if I convince her to leave, won't she join the Followers of the Apocalpyse, who the BoS will kill in the process?

Also, what is the 'farm-tech' path?

Pretty please (with sugar op top)?

In my game, i left the old elder in, killed house, took over NV, and there was NO mention of BoS at end!??!

She'll try to join at an outpost at an abandoned railyard, and those annoying paladins will slaughter them. You don't have to worry about Julie or Arcade getting killed.

The farm-tech path involves going to Vault 22 and acquiring data and runs alongside "There Stands the Grass". The result is exactly the same as the pulse gun.