Am I using the right terms in referring to "soft" and "hard" vowels and consonants?

There is no universal technical meaning for 'hard' and 'soft' when it comes to sounds. You will not find it used by professional phoneticians.

However, within many languages, there are pedagogic conventions for describing hard and soft sounds that do not translate across languages. This is often done in an overlap with orthography.

For example, in English people speak about the 'hard' and 'soft' 'c' to differentiate between /k/ in 'cup' and /s/ in cell.

This is very different from Slavic languages where 'soft' and 'hard' consonants describe pairs that are palatalized or not. As in /d/ vs. /dʲ/.

Sometimes, this applies to vowels. In Czech, for instance, there is a traditional distinction between 'hard y' and 'soft i' which is now only relevant to orthography - the preceding consonant is palatalized for soft i. However, this refers to a perceived difference in the darkness of the sound which is still preserved in Russian. Czechs will also describe 'ü' in German as hard y.

As you can see, there's no easy way to map the idea of 'hard' and 'soft' when it comes to sounds across languages. However, there seem to be certain tendencies in how people describe sounds across cultures. Certain voiced plosives are more likely to be seen as dark or hard whereas affricates are more likely to be seen as soft or light while voiceless stops may be seen as sharp. This is a whole area of study called 'sound symbolism' or 'phonosemantics'.

The way you used 'hard' and 'soft' is very idiosyncratic but in the context of a conversation, it may be understood by people. But only if there's enough context.