You've sent me running to my Anna Butterworth book Harmony in Practice
. It mentions the various different ways to use a 6/4. The one I know best is the 1c V 1 progression. It's important to keep the 5th in the same voice through the Ic and the V - the 6/4 and the 5/3. Okay you're helping me remember now -
1c V (1c on a strong beat). The 5th is doubled so creating the same note in two voices which are held through the 5/3 chord.
Ib Vc 1 (Vc is on a weak beat). The soprano is three steps up with the same pattern contrary in the bass. The Vc is like a passing note/chord with the 5th in the bass and the soprano.
The summary on p93 reminds you to double the bass note in a 6/4 chord. So yes - go for it and double the 5th.
A think a good tip is to remember to use lots of stepwise movement to make good voice leading if you can and to use contrary movement if possible.
Don't have nightmares about consecutives!