Another 'good for you' for being proactive about this!
It's far better to learn about it & avoid causing the problem than to have to manage the consequences!
So much lush grass could well be a problem. If he's on the 7 acres alone, he won't have help eating it, or company to motivate exercise. I would personally want to find him some company of another horse or few, and consider making a track around the paddock(google 'paddock paradise' for ideas) or at least strip graze to reduce the amount of grass available to him.
As already mentioned, keep a close eye on his weight, because 'grass founder' & insulin resistance type probs are generally due to too many calories, so don't let him get overweight & this will reduce the risk of lami. Don't wait for signs of 'fat deposits' & cresty neck, because that means it's already a chronic problem by then.
Feeding him grain is another potential source of problems. Generally speaking, grain, being high starch/carbs is not a good feed for horses. If it's not well processed, it's also very hard for their stomach to digest. Often 'hard feed' is also sweetened with molasses or such, which is another thing to avoid. Potential for problems are higher if the grain is fed in large &/or infrequent meals. So I'd consider carefully if you really want to feed it at all(if he needs more weight/energy there are other alternatives) and if so, feed it to him little & often rather than only a couple of feeds daily. If he's healthy & a good weight, I probably wouldn't bother with anything other than a ration balancer or such for nutrients, as chances are the grass & hay will be well enough for him. Katy Watts | Safergrass.org
is a good source of info about grass/feed as it relates to laminitis and hoofrehab.com is a good resource on all hoof related considerations.