I bought the following about a year ago, but never got round to making use of it to LEARN to foil

115+ fuse, 75 fuse
900, 800 front wings
330 and 255 back wings.
95 mast.

I now realise I could configure this to be:

1. Starboard GT, 800 wing, 75 fuse, 330 back wing (but with 10cm higher mast)
2. Starboard IQ, 900 wing, 115+, 225 back wing shimmed to -2
3. My own setup of 900 front wing, 115+ fuse, 330 back wing shimmed to -2

So far I just tried tiny hops on the 3rd setup, which I thought would be the easiest. Now I realise the 330 back wing might be a bit too powerful a combination. This on 91cm wide AHD thunderbolt.

My goal for the moment is just to get comfortable with level flight, and take it from there.

What combination is likely to be the easiest? Is it worth getting 255 -2 or one of the shorter fuselages to achieve my INITIAL goal?

I would go with option two. I don't think you need to get the 255(-2) for now. If with option two you feel you need too much board speed to get flying, use the +0.5 shim. If it's too powerful (lifts too fast or breaches), put the -1 or -2 shim.

Agree with WillyWind. Also the 75 fuse is going to be a challenge with the small wings. 115+ is a lot more stable but powerful. 105+ has a lot of the stability but less powerful.

I hardly ever bothered with even the 95+ as I didn't like the lack of stability.

I learned using option 1 on a modified slalom board, but there weren't many options back then.

I agree with all above feedback.

I would just add:

1) tiny 0.5 adjustments in shim make a tremendous difference. therefore 0.5 is the difference between your board getting "elevator effect" to which you need to compensate with weight shift with speed vs no need for shift because the foil shoots only forward.
Here are more details for my specific setup (also Shim recommendations from Starboard):
Here is the difference discussed on NW Windtalk posted by me in December 2020 (over 3 years ago):
"Starboard Race Foils with Fuselage 115+ & 115++ adjusting the shims"
groups.io/g/nw-windtalk/message/70252

2) It may be easier if you want to learn in lighter winds (lower take of speeds) if you can get your hands on M1000 or FR1100
I tested them and compared them in the following post:
"Starboard M1000 (Millennium Race) wing vs FR1100 (Free Ride) wing"
groups.io/g/nw-windtalk/topic/81678026
In that post there also some more comments from our Local Winduro & City Leage Champion: Jonathan R in case you are interested.

Yes, that long fuse 115+ (on SB FW & Race type board) & 115++ (on SB Go) with 255(-2) stab when properly shimmed is so stable and wide range that I would recommend it to anyone who is comfortable with planing speeds (coming from windsurfing background).

For someone who never windsurfed before, there is a value in starting from "larger shovels" like Slingshot i76, i84 i99 (depending on your weight). Because you are learning to fly at lower speeds (though more "elevator effect" when the gust hits you).

You are on the right path and you do not need to fly high. Even "skipping stone" and "foil assisted planing" is a safer way to learn foiling, how you want it, when you want it. Then take higher flights, if you want it.

I also used option 1 while learning. It felt a lot like using a fin pushing against the foil with the back foot. The large stabilizer helps control the short fuse. Good for reaching. As I progressed I also switched to the iQfoil set up and really like it. Incredible angles upwind/downwind. Use it with the 800 wing as the wind increases or you plan to sail reaches Might be a good learning option too