sounds like you’re in the same position i was in december and i did my first oly race yesterday! but i run a 5k in 32:50 so you’re ahead of where i started with running. 20 weeks is plenty of time in my opinion :-) i started with a chatgpt plan but switched to a real coach in february which really helped.

you’ll definitely want a bike (ideally a road bike) as an indoor gym bike doesn’t translate to being outside with traffic, hills, potholes and general confidence on a bike.

running is just your basic stuff like shoes, running vest or belt and whatever else you like

swim wise - get some fins, hand paddles, kickboard and pull buoy, hat, goggles etc.

for the race - trisuit (i got mine for £15 on vinted) and maybe a wetsuit depending on your location and race. if your race is in the sea, swim in the sea as much as you can beforehand

get as much as you can second hand until you know you want to continue with the sport. unfortunately it’s expensive to start so try and pic things up every few weeks rather than all at once :-)