Gripboard.com for learning about grip/lower arm strength.
Grippers are good for crushing strength, I recommend Ironmind captains of crush grippers.
Pinch strength- get a couple of 2x4's, nail them together to make blocks of various widths, wider the better, screw a eyebolt in and attach weight. Pinch and lift as long as possible. Also pinch 2 weight plates together smooth side out and lift, 2 45's is a super strong, 3 25's is world class.
Supporting strength- rack pull and hold: rack as much weight as possible, lock out ( deadlift) and hold untill grip goes out.
Ironmind sells a product called eagle loops, straps with finger loops that can be attached to a bar for deadlifts or a chin bar for hangs.
General lower arm strength- wrist roller. Make one yourself out of 1.5-2 inch pvc or steel, wood, whatever you have around. drill hole and attach some good strong cord and tie weight to the end. stand on chair so the weight is hanging. hold arms straight out and roll the weight up. Works wrists and forearms.
Many other things can be for on specialist sites like the one mentioned above. Grip/lower arm strength is my other hobby.
For benchpress don't forget supporting groups like someone else said. shoulders, and triceps are extremely important in big benches. behind the neck presses to ear level are awesome for strong shoulders, go for weight here. Triceps- close grip bench, pushdowns, french presses, are all good. Also for someone as tall as you try benching with your grip as wide as possible. Less travel to chest and lockout. might feel awkward at first but work at it. Stay tight, grip the bar (squeeze). Feet flat on floor, butt on bench, shoulder blades on bench, squeeze them together. back of head on bench. Don't bounce or bring butt, head, shoulders off bench, stay tight! Don't over work muscle groups, 1-2 times a week, many powerlifters bench 1 day, squat 1 day, and deadlift 1 day. need time to rest.
For gaining weight eat like you normally do but add good quality protein snacks. boneless chicken breasts, cottage cheese, milk, legumes, TUNA, protien powder. Try to get at least 1 gram of protien per pound of bodyweight.
For exercises to do at home. Pushups: work up to 1 arm,1 leg pushups and you will be very strong. pushups on fingers ( mentiond already). Chins. Pistols ( one legged squats). Dips ( if available). I'm not proofreading this so I hope it makes sense. PM me for more details.