Correct, except for Duolingo purposes "αυτό το βράδυ' is more accurate because of better word matching (this - αυτό το). And απόψε is exactly 'tonight' of course. But in real life, you are right on the money!!
I am a bit confused, in Cyprus people use απόψε for the hours between c 6 and 11 and say καλή νύχτα when you are leaving. I always translate απόψε as this evening and νύχτα as night? But Duo seems to translate both νύχτα and απόψε as night.
Νύχτα is both night and evening - if it's already dark. Βράδι is evening. Απόψε means tonight or this evening.
If you click on the word απόψε if gives both tonight and this evening as the translation but if you use this evening in the translated sentence, it is marked as wrong.
The "-άρω" ending comes from the Italian "-are". Quite a few verbs of this kind are part of the Greek vocabulary:
μοστράρω=to show off sth
γουστάρω= to like (sth/sb) a lot
There are also verbs of Greek origin ending in "-άρω", an example being "κριτικάρω"=to criticize
The endings of the past (aorist) tense are:
1st singular: -ρα
2nd singular: -ρες
3rd singular: -ρε
1st plural: -αμε
2nd plural: -ατε
3rd plural: -αν
The verbs that get the "ε-/η-" prefix in the past (aorist) tense are those ones which are stressed on the first syllable, for example: παίζω, τρέχω, κλαίω, δείχνω etc.
On the other hand, verbs that are not stressed on the first syllable don't get that prefix, for example: πετάω, περπατάω, μιλάω, γελάω, κοιτάζω, διαβάζω, σκοράρω, μοστράρω etc. Please note that this is a rule of thumb and there are some exceptions to it. Hope this helps!