How low on the chest...
Generally speaking from my experience as a 285+ bencher at 180, you should touch to your upper abs while tucking your elbows so that there is a straight line between your elbow and the bar, and your elbow is vertical at the bottom.
As for pressing off of the chest (I assume you mean sternum/nipple area?), if you want a shitty bench press, an inflamed bicep tendon, and many pec tears then you can press off of there with a wide grip. As for how hard it is, it depends on what is muscles are strongest, and your proportions. I have very long arms, and very strong triceps and deltoids so my wide grip bench (pinkie on the power rings) is less than my competition grip because I can't use my triceps and deltoids as much.
Personally speaking I press very wide as legally possible in completion which is index fingers on the outer rings. I find this initial press off the chest first 2-3 inches is very easy and then I hit a sticking point. I am working on pec strength to bring it up now and speed off the chest. As for how long you can touch on the chest depends. If just training there is no rule. So touch and go, paused and long 3 second pauses I incorporate all. If speaking from a PL perspective you touch untill the judge says press period which varies.
I press wide, as weight increase, my hand width moves in slightly. it really boils down to personal choice. Who are you competing against anyway? Personally, I'm my best competitor and frankly, ALL of my goals have been meant. At this stage of my life, I lift mainly b/c of the job I have. Strength plays and has a BIG factor when dealing w/large PT's in the operating room.
Wide grip is essentially used to reduce ROM between press and lock out.
How low should you press? Well you need to do a pause rep in most federations, so it'd make sense to be touching your chest at the bottom of the lift.
Harder/easier comes down to personal preference, personally I get shoulder pain pressing wide and have always trained close grip even when I first started training BB.
I've actually evolved into a narrower press than I used to. It allows me to train more frequently while keeping my shoulders happy. And I've always had strong tris anyway. But I've gone from index fingers on the rings to hands equally spaced between the rings and the bare spot.
When viewed from the side, your forearms should stay vertical. That means where you touch on your chest should be dictated by how much you tuck in your elbows. The more "tuck" the more shoulder involvement and the lower on your chest.