Well, HH is primarily an adult visual novel, the porn is more of a side thing, though I made sure to get to the porn stuff quicker than most visual novels because I understand that some people are only interested in porn at first. But that doesn't mean the porn is neglected here, it's just not the focus of this game. There's still more here than most games of this type though!
The farmable garden is a new feature to v0.18, that's been in the works for a few years. That will allow you to grow +3 Lust crops and x3 EXP crops (those will make leveling stats faster for each character). This, and leveling the bar are great things to focus on to ensure you get the most out of your playthrough.
I don't have a set plan on how much content there will be in game, I just plan for the story to come to a fulfilling conclusion, and for the rest of the game to be fun and fleshed out as well. I care deeply for this game and the characters, so I want it to be very good by the time it's done. I would guess that the story is roughly 70% done. But this is assumed with only a destination in mind, and not the whole thing mapped out.