Cue bidding may be initiated as soon as a trump suit is agreed.
Should not be employed in either 2C sequences (control requests are used here)
Neither with 3-suited hands (elaboration of 3-suited hands takes one to the 4-level) therefore ERKCB with 6 or 7 KC! is easily superior.
Important Note:  TURBO is tightly integrated with cue-bidding.

 The 3 Guiding Rules of Cue-bidding

1. The first rule is to announce cue bids with minimum of passed over bids
2. A corollary of the first rule implies a second rule: that any bid passed over, is an indication, that that suit had no valid cue-bid that could be made
3. The third rule is that a trump suit must be known by both partners
4.  A first  cue bid made at the 5-level must be either a Void or a Singleton Ace
5. At any level a cue-bid made in a suit already cue-bid by either partner  may be  either  Ace or King unless made in an opponents suit in which case it must be showing either an Ace or void.

Cue bidding below level of game in the agreed suit

The following are eligible for cue bids and they are of  equal priority:
Now a couple of additional rules:
The trump suit is not cue-bid - all other suits can be. In fact returning to the agreed trump suit below or above game simply indicates no further cue-bids to show.
Bidding a Major or minor game in the agreed suit is special - simply indicating that the Q of trumps is NOT held.
A cue-bid should not bypass game level unless Queen of trumps is held and game should be bid if the Queen is not held.
This  does not forbid a partner to continue still having belief in a slam - he is aware his partner does not have the trump Queen, there again he might possess it himself anyway!
Obviously TURBO comes into play after a major game is exceeded but prior to reaching a minor game. The TURBO  rules  comes into effect  at this juncture:
4NT should be bid if an EVEN number of KEY cards is held (that is 2 or 4)
If an ODD number of KEY cards is held 4NT can be bypassed (that is 3 key cards) and a further cue-bid or agreed suit is bid.

Cue bidding above level of game in the agreed suit

Now the eligibility of cue bids is tightened - this applies to both Major & minor slam bidding:
A 5NT bid is special - a grand slam try. Its a sanity check on the trump suit! Responses are: