Long spans of notes

There are a couple different ways this could be done, depending on how you'd want it to come out on playback. There are, after all, too many beats in that measure as notated.

But the things you will need as multiple voices (see Voices in the Handbook to understand how to have different notes sounding at once), also Tuplets - that long string of apparent sixteenths should probably be entered in Notes / Tuplets / Other as 28 notes in the space of 4. You can hide the number and bracket if you like. You will also want to see the Handbook under "Cross staff notation".

You'll still end up with too many beats in the measure, so you'll neeed to right click the measure and choose Measure Properties then change the actual duration, and hide the extra rests that will display.

Depending on exactly how you envision this, you might put the whole note in voice 1, the other notes all in voice 2 top staff, use cross staff notation to push the first few into the bottom staff, and set the actual duration to 6/4.

The simplest way is possibly just to make two bars and hide the time signatures.

Enter the top stave notes.
Enter the bottom stave low F in Voice 2 (note length 9).
Enter the lower other notes in Voice 1 and then use [Ctlr][Shift] arrow to move them to the top stave.
Enter the 8va (to the bottom stave!, of course and then move it up)
Add the dynamics
Change the notehead of the bottom F to semibrieve.
Make the rests invisible.
Make the dot on the lower F invisible

You might notice that I've added some grace notes at the beginning but this was just to make it easier to show the ties/slurs leading onto the first notes.