The 2019 Slingshot Infinity 76 comes with a 60 cm mast. That's fine to get you started. You can get the longer mast for about $150 after you've gone through the first few sessions.
There are quite significant improvement in the foils going on. Typically, getting a newer foil will give you a significantly better foil - but last year's foils can often be had for half the price. If you go with an older foil, you'll pay with a slower progression. But pretty much everyone who's an experienced foiler now learned on older foils

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I have seen maybe 10-20 windsurfers foil for the first time. Almost everyone got up onto the foil during the first 30 minutes when the conditions were ok; some got up during the first one or two runs. Learning to control the flight takes a few more sessions. I'm a slow learner, and it took me perhaps 8 sessions to stay up for 1000 or 2000 feet. Faster learners get there sooner, slower learners (or someone on unbalanced gear) may need longer. But you'll probably have the feeling that you made decent progress after most of your early sessions.
We just got our Infinity 76, and I went for a session where the wind dropped in the middle. I just got a couple of flights at the start, and a few more after slogging for 45 minutes before it got dark. I probably could have been planing the entire time on my large slalom gear, but I had rigged small (5.0) thinking the wind would stay up or increase. Still, I found myself driving home with a huge grin on face - much bigger than after most windsurfing sessions.