You keep any angels investors you still have actually boosting revenue. Anything you spent on an upgrade is considered sacrificed - you won't get those back, and you don't keep those upgrades through a reset.
An easy strategy early on for resets is to reset once your angels to claim matches or is higher than your angels in hand. So this means you're doubling your angels, or more, once you hit reset. The game will even highlight the investors option on the menu once you hit this point.
Since it takes time to really build up that gallery of angels, and sacrificing them for any given upgrade means you lose that income boost from the angels you spent, the game warns you before you try to purchase any upgrade that costs you angels. It no longer gives a warning if the cost in angels is less than 1% of what you have, considering that a negligible cost (so for the angels you say you have, sacrificing 2 angels would generate a warning, but just one wouldn't). Only spending when it doesn't warn you not to is another easy early strategy.