I'll ask the questions...

What size board Starboard start
What size fin
What size sail
How much do you weigh

Wind speed required for planning depends on many of the above. Can provide rough estimates based on what suits me...

Harness is not essential, but it will make life much much easier.

Which way is the board trying to flip toward your feet or the other way

No such thing as a silly question.

To get into the back straps you need to be really moving fast. If you are not planing full, with the rig raked back, then dont go for the back straps.
You will need to get a harness and learn to use it if you are ready for footstraps.
First you need to go fast, then the harness, then the straps. When you get more skilled you can change the order of these, but until then.....
Concentrate on getting planing and harness technique. Straps will come as a consequence when one day you look down and find that your feet are naturally placed close to them anyway.

JB