Hi Franzi, cool, welcome to the wing club - well I think you would be fine with the 1750, my wife learnt on a 2000, but that was too big very quickly, she went from there to 1500, 1250 and now comfortably on 1000....gybing practise level/50kg. High aspects it depends on how high aspect they are - the more radical ones look almost straight with no raked back tips, these are great for pump foiling, but not ideal for beginners - our Aero High Aspect are not that radical and very much aimed at learners in the 1500-2000 range. So I think you would be fine there, add a 1000 or 1250 wing set later. For first lessons or attempts, the 5'4" will be quite small, but for sure a good size to progress on once the basics are there, my wife (and myself) both used these for the first 12 months. She is now on 5'2/85L, whilst I generally ride a 5'0"/75L, I weigh 76kg's.
2400 Aero Lift is also an option for the first steps, but I think you will outgrow that very quickly. We always reccomend getting a lesson if at all possible, as the progression is mostly very quick, which helps to keep the amount of gear changes less than windsurfing for example.