Hmmmm.... the Rio S at 175 liters does not seem (based on the volume) to be significantly smaller than the 180 liter Naish Kailua, but take a look at the widths.
Kailua is 85 cm wide..... Rio S is only 75.5 cm wide.
That's quite a difference for an 83 Kg.(183 lb.) sailor.
As far as the forward footstraps, I think you are going to be disappointed here.
For a fairly heavy sailor, on a fairly small board, standing forward on the board to get into the footstraps isn't going to get the nose of the board up high enough for the board to plane really easy and freely.
So, you can try the forward footstraps (be very careful if you use the ones way up by the mast foot as the footstrap can trap your toes as the mast comes crashing down on the footstrap perhaps resulting in a foot injury), but getting into the foot straps, before you are hooked into a harness where you can transfer your weight off your feet, really isn't going to give you the full meaning of what footstraps are all about.
If you have your full weight on your feet, you don't need footstraps.
When you have your full weight suspended from your rig, through the harness/harness lines/boom/ mast and are developing full mast foot pressure THEN you need footstraps.
Hope this helps,