1. Skarlet cannot dash into U3, 4. She can only dash into U3. A small solution to this is to tap Block after dashing then let go and do U3, 4. It shouldn't really be used outside of wall combos.
2. Skarlet does not gain meter from an Up Slash after a Red Dash if you hold forward or press any button between the Red Dash and Up Slash. Since meter is very important to Skarlet, what you have to do is let go of forward and press F2 for Up Slash.