1 . It's similar to how you can use either simple present or progressive in English to express the same simple present in Spanish, though the simple present is the closest translation.
I eat it. (present)
I am eating it. (present progressive)
I guess it also applies with the preterite. Please feel free to correct, anyone though.
I ate it. (preterite)
I was eating it. (preterite progressive)
2 . The simple present tense of "elegir" for the "nosotros" form is "elegimos". But its preterite tense is also "elegimos", so without context, the verb in the sentence above can be treated as either present or preterite.
Elegimos los colores juntos.
We choose the colors together. (present)
We are choosing the colors together. (present progressive)
We chose the colors together. (preterite)
We were choosing the colors together. (preterite progressive)
It would be eligiendo (it's irregular), but Spanish doesn't use the continuous tense very often.
In real life, you'd probably have enough context to know if it is present or past. Every language has ambiguities; we generally rely on context. If there isn't enough context to be sure, you can add a time word (ahora....ayer....el año pasado).
I thought you must have had the female voice, because dropping the final -s is a common complaint for that voice, but I see the male voice does it on this sentence, too. Just know that this is very common in natural speech.
There is a sound there, a sort of aspiration (kind of like the English H) that wouldn't be there otherwise. With time and practice you can learn to pick up on that, and your brain will start to accept it as a replacement for s. I have to concentrate now to even notice when -s's are "swallowed," because I'm used to it from speaking with native speakers.