Slitherine

Rules, p38, First bullet "Any unit making a forward move...."
Second Bullet " The unit makes a forwards move and both corners move at least 3MU........"

Question : When sliding sideways combined with movement does the unit first move at least 3MU then slide ?

or does the unit have the option of sliding sideways before completing 3MU forwards?

We play it that you can slide at any point in the move. Somtimes this is halfway through it if you need to slide to dodge terrain or other friendly units.

I agree and there is only so much you can do with a forward move and a lateral slide. But what about wheeling and sliding to thread a path among impediments to movement?

As long as both front corners move 3MU that move can include a slide and a wheel - as long as the entire move is more than 6Mu from the enemy.