Your translation is correct.

1a) There’s an à because there is indeed an expression viser à [verbe] "aim to do", which is an omission in WordReference.

1b) Unfortunately in this case you’d have to check more than one dictionary and hope that one of them has it. In this case, Reverso does:

viser à         v
avoir pour but de

I realize this is frustrating since it suggests that any time you don’t find an entry, you might find it in another dictionary. I think that would be fair to conclude, though I tend to use different dictionaries for slightly different purposes to reduce redundant checks, and your choice made sense for a two-word entry – I’m surprised that WR lacks this expression that Reverso has. I just used their "signal an omission" form to request this entry.

1c) No, not only because (as you now know) viser à is a fixed expression, but also because the construction pour [verbe] is better translated "in order to [verb]". Hence we’d get something like "aiming in order to [verb]", which doesn’t work in either language.

On the other hand, you could say, for example, « viser à terminer avant 15h pour vous permettre d’attraper le bus » : aim to finish before 3 p.m. in order to allow you to catch the bus.