As a conjunctive adverb with a consecutive meaning, similar to folglich or deshalb, also can appear in the first position of declarative sentences.
Ich denke, also bin ich.
I think, therefore I am.
Die Arbeit hat mir nicht gefallen, also habe ich gekündigt.
I didn't like the work, so I quit.
Es nicht zu schaffen, war keine Option. Also habe ich es geschafft....
The first sentence is only valid if also is refers to ich:
Also ich habe es geschafft.
which roughly means "I made it (but maybe others did not)."
This way, Also and ich together are the first part of the sentence, followed by the verb. Otherwise, the verb-second rule would be violated.
In the second sentence, also applies to the statement as a ...
That are two questions.
Would you say there is a difference between was für ein vs welch ein when you want to express amazement / surprise?
There is a difference. But I think almost nobody will notice and maybe at least some will disagree and call it bean-counting. Welche is asking for characteristics. Welche Eigenschaften? - What attributes?
Was für is ...