Hello and welcome!
This is the advice I wish I had gotten when I started:
Small is less forgiving and immediately limits your firshy choices (first fishys, just made that up!)
Large is expensive. It can be very costly to find out the hobby is not for you.
So, hit gumtree! You will need a man with a van, but for me I can get decent mid range starters, around 3ft wide, 18" tall so suitable for young angels for example. These tanks typically cost £1 per litre in size around me second hand, but normally have everything you need to start tropical.
Once you have decided the hobby is for you, get the best you can for the money you can spare, but dont go nuts, you can do this with still being savvy.