Learn English – Using three examples with “range from”

At that point I'd probably pick out one of the list for special attention using "not only ... but":

There are several recommendations I have to further improve the sites, not only to improve their profit but to decrease their cost and improve their usability.

I'd cut that down further, though:

I have several recommendations to improve the sites—not only to improve their profit, but to decrease their cost and improve their usability.

Careful (not to say pedantic) speakers place 'only' directly in front of the word or phrase it qualifies. So they would say: "I drink only water." The claim is that saying: "I only drink water" could be interpreted as meaning: "Drinking is the only thing I do with water, not washing in it or playing with it, etc."

In theory there may indeed be cases where the placement of 'only' is a source of ambiguity. In practice, however, it is unlikely that anyone would be confused, particularly in spoken language where intonation contributes to meaning.

"We have only seen a few of the sights of this marvelous city" sounds perfectly natural to me, a native speaker. In fact Google returns 3 times as many hits for "I have only seen ..." as for "I have seen only ... ".

As an aside, the sentences are in the present, not past, perfect. But the tense of the statement is irrelevant to considerations of where 'only' should be placed.