eyes I agree with euro. My clinic says of day3 embryos only about 30% will be chromasomally normal. By day 5 this is 70%. So if you wait you can hope to choose the best ones. But if you don't have many there's no point waiting.
Assisted hatching - for repeated implantation failure, and yes, a great deal more expensive. I think you said you've had a m/c? In which case implantation is probably not the issue.
Protocol. I am overseas and can have a lot of choice over treatment. I did short protocol because - fewer drugs, shorter time, cheaper, no apparent reason for the usual long protocol. Most clinics seem to push LP in younger patients/good amh but it's unclear why. I suspect a lot is to do with it making it easier on timing. I hear stories that in some uk clinics they only do EC on a Thursday, or not at weekends. I wouldn't go somewhere like this if you can choose - when your eggs are ready they are ready. My clinic said you get on average one extra egg on SP, but slightly lower preg rate? I don't know. We had 11 eggs, 7 fertilised, 4 made it to day 5, my one put back was graded 'good/fair'. (I'm 30) It's a lot of guesswork....
Yes, it is very scary at each stage thinking you might have none left if you keep waiting. We had never conceived before, so I thought - I'll get crap eggs/empty follies, I'll ovulate too soon, they won't fertilise, they won't divide.
Honestly, I forced myself to only look one step ahead and see each step as a victory even if we didn't get a bfp - ie at least we can get fertilisation etc. I am still in that mindset and don't really believe I might have a baby in 7.5 months. Just still one step at a time.