TBH in your shoes I would get the fish on your next days off (so you can watch for stress) a single fish will produce minimal ammonia the bacteria will be ready to take on his poop by now

Your biggest enemy will be you feeding, thinking his hungry and the wasted food producing the excess ammonia/waste. it will have a tiny stomach and will do just fine with 3-4 feeds per 7 days.
Regarding water changes leaving the water to stand for 24 before water changes applies to big water changes 50% or very expensive/fragile fish.
Little and often from the tap drop of prime boom done. maybe 20% water change per 7 days (call 3 litres), problems start when you lazy and think sod ill miss a week and try 40 % the week after, your chemistry goes all over HTH
