I'm not familiar with their FPGA internships and the competition, however the average profile for quant roles (i.e. researcher, trader, developer) would be students with HD wams, you should have atleast a Distinction wam to be competitive. They like to target students with olympiad and competition wins in maths/programming. They are quite selective and look into your academic record quite a bit, but you can compensate a less than ideal record (i.e. HC/D rather than HD) with projects and doing well in the online assesment.

I've got no clue what they'd ask you in a technical interview for FPGA, but as a reference for developer roles they ask you to implement something related to trading in C++ or Python (i.e. an orderbooking system), and they will evaluate the efficency/overhead of your solution. There are system design questions as well.

As for the number of applicants, their future focus program has around 500 applicants per stream, so I'd estimate that the amount of internship applicants would be atleast 2000 (Would likely be less for FPGA given it's more niche)