Given your ambitions are to one day get into investment banking, it would be more suitable for you to consider starting your career in a big four accounting firm.
While not identical, the working conditions, corporate acumen and hours worked in a big four will be a good initial taste of what's to come should you really want to go into investment banking. Working at a mid-tier accounting firm might not have the same level of transferable 'skills'.
You will likely require an additional qualification once you've completed your ACA, I suspect this will need to be a MBA to join an investment banking firm as an associate through their post-graduate route. Individual organisations may have their own policies.
It might be possible to join some organisations as an analyst, however many firms will be highly selective based on academic institution. Others with direct experience of this might be able to provide more information on whether ACA would be sufficient.
Goes without saying, but careers in investment banking are extremely competitive. Big Four accounting firms are also extremely competitive (though not to the same extent), which combined with other factors will give you a good taste. It is vital you pass all ACA exams the first time, to give you the best chance of success.
I've only done a short summer placement in investment banking. Know a few colleagues who took that route full time. They joined as undergraduates through a summer placement and then after University got their full-time jobs as analysts.