The usual construction is "to be so kind as to do something". In your example it would be:
We all know it is a long way to their nearest office, but they have
been so kind as to arrange for them to come to us.
This construction seems a little odd at first, but as @FumbleFingers says below, it means (approximately) their kindness was so great that it caused, enabled them to help (i.e. - so = to such an extent).
Out of your 4 sentences, three are correct. The only one that is not correct is:
Until you called me, I'd visited a store and bought some foods.
Until is used for to specify a duration going on up to the point specified by what follows until.
In the following sentence, the action of studying for about 3 hours had been going on up to the point where the speakers was called.
Until you called me, I had been studying for about 3 hours.
The same sentence, but with before, is also correct, but there is a difference in meaning. The studying here also took about 3 hours, but it had already stopped at the moment that the speaker was called. So, the caller did not interrupt or stop the person studying:
Before you called me, I had been studying for about 3 hours.
The third correct sentence is:
Before you called me, I'd visited a store and bought some foods.
The action was completed before the speaker was called. This is the reason that until cannot be used here, because that would mean the action had been going on up to the point where the person was called. The past perfect had visited here implies that the speaker had already finished the action of going to the store to buy food.
Best Answer
You're looking for any of:
"This had been checked and then sent to you." or
"This had been checked before it was sent to you." or
"This had been checked before [I, s/he, they, Sally] sent it to you."
Either there needs to be a subject for "send" (whomever is did the sending) or that part also needs to be in the passive voice. And since the sending happened in the past, it needs to be in the past tense ("sent").