First - WELCOME to THT!

Lots of great folks and info on here!
At 1,950#'s (dry) + a 60gal. gas tank + "family" + water toys + ice/drinks + misc., I'd be reluctant to put a 115 (2 OR 4-stroke) on that boat - especially for skiing! A "115" is gonna' really burn some gas trying to "ski" and the hole shot needed for it.
That 18 is a HEAVY boat and NEEDS a "150", IMO - a "140-150/4-stroke" would be a PERFET match for all you want to do!

It will push the boat a LOT more efficiently, the motor won't have to "work" as hard, and therefore, it will last longer!
Not much more frustrating than being "underpowered" or if you decide to sell it down the road, the "140 or 150" would be more desireable to a buyer.
I think the "max hp rating" on the "18" is 150?
NICE boat - good luck!
Regards,