can i shuriken flip one unit into a contested battlefield and move another, readied unit at base to that same battlefield at the same time?

No — you can't bundle a spell-move with a Standard Move, and by the time one of them lands, the window for the other is already closed.

Only Standard Moves can be performed simultaneously (multiple units to the same destination as one game action, Rule 144.3). Shuriken Flip is a spell on the Chain — it can't join that declaration, and while it's on the Chain the state is Closed (Rule 144.1.b).

Even sequenced back-to-back it fails: the instant a unit arrives at a battlefield you don't control, Contested is applied, and the following Cleanup immediately stages and opens a Showdown/Combat there (CR 323.7–323.12). Once it's open, Standard Moves are banned (Rule 144.1.c) and Shuriken Flip can't be played — it has no Action or Reaction keyword (Rule 343.1.a). So whichever you do first, the second unit can't get in before the fight resolves (FAQ #12450). If you want two units to arrive together, do one simultaneous Standard Move with both units (or Ganking) — no spell required.