I have been using a 6 metre Cabrinha x2 wing, a 6ft 8 JP 95 litre foil board with a Neilpryde XL foil with 65 cm mast.
I am 78 kgs in weight too.
I think the Neilpryde XL foil wing is around 1900 or 2000cm2.
I love using it in 15 to about 19 knot wind. But not more because it decreases my upwind ability.
In 19 knots & over I'm quite sure it will be better with a smaller foil wing like my 1600cm2 Large.
Or I could go to my original 4 meter Naish Wingsurfer which is much easier to handle in 20 to 25 knot winds and feels better for upwind ability. But have yet to do a full comparison.
If I was in your position. Then yes try to shim the stabilizer because it is the cheaper option.
I think maybe just go a size smaller in foil wing size than what you have currently. I think it is too big a foil for anyone under 85 kgs.
But technique like knowing how to instantly put weight on front of board or point more upwind or depowering windwing will lessen the chances of breaching. So a larger foil & windwing will give a learner plenty of this practice like it has for me so far.

I still cannot jybe whilst still up on foil. But believe it wont be long in the right conditions.
Good luck & enjoy he challenge.