I'm not the highway king, or even the daily milage king, but I took 2 trips from Illinois to the west coast and back in 2012 and 2014. Crossing the country, I averaged over 1000 mi/day, and gained some perspective regarding what makes a good road car, etc.
Almost nobody is going to want to use their car like I did (and will continue to) on those trips, but I've got a few observations.
Teby (who no longer stops in here much) made fun of me for waxing on and on about "touch points", but it's my personal belief that how comfortable you are every place you are touching the car is going to determine a lot about how you feel about driving it 1300 mi/day. If your seats hurt you in 200 mi., they're going to become instruments of torture after that. Similarly-- how is your position? Richard noted that the wind batters him around to the point that he's done driving after a couple hundred miles-- that can be corrected by getting behind the short windshield, and building a wind deflector to go behind your head (try it, you'll never go back). Cool weather, top down driving can be comfortable if you have some sort of hard side-curtain or roll-up window (shameless IM plug there) to stop the wind intrusion. Lots of guys have made nice acrylic side-curtains, and @Troy Sloan makes and sells "cruising windows"for this purpose. If you have comfortable seats mounted low enough in the car to get you behind the windshield, you have an effective wind-deflector behind your head, and you have the side curtains (or windows) - you can drive all day and into the night.
It's the same deal with the steering wheel and shifter - the places you touch the car. I'm a silverback gorilla, so even low in the car, I like to rest my left forearm on the top of the door, and rest my right one on the wheel.
I've gone on record as being one of the lone doubters regarding crazy-low tire pressures. I've tried it, and there's just no way I'm going to try to run 20 psi in my tires on purpose - the handling becomes a squishy, squirmy mess to say nothing of the terror I feel running half the rated pressure of the tire. I'm also very reluctant to add weight to a car that already seems too heavy for what it is, but I've got the "big tank" option, and carrying the extra fuel up front really does help. I'd like it to be lower and further forward in the car, but that creates some safety issues that most people would not be able to live with (the car becomes a bit of a bomb in the event of a front end collision like @Lane Anderson had).
The alignment and ride height are very, very important (like @DannyP said). Lower is better. Your car will become less of an airplane wing aerodynamically and you'll be less susceptible to cross-winds. There's a limit here, of course - but it's one of the reasons I dry-sumped (insert joke here @Robert M) my car - making the sump no longer the lowest point on the car gave me the confidence to drive it across time-zones without worry of emptying my oil on a pebble in the road. Nobody else is going to do this (even if they should), but you can get pretty low with a CB "thin-line" sump (and please do run a sump - the stock oil capacity is a joke).
@Sacto Mitch wondered about the "happy place" with engines. There's a school of thought regarding engine speed that advocates running 4000 RPM on the highway - the idea being that the fan speed at higher RPMs provides cooler running. I'll buy that for spirited drives in high-load situations (driving like a hooligan in the mountains) - but in my experience on the Great American Open Road, running higher RPM makes the engine run hotter. The absolute sweet-spot is about 3000- 3400 RPM. If you really, really want to drive 80 and you have a .89/3.88, you'll run hot.
And here's where I stand alone in this crowd. I'm not sure that having an engine that will last 100k mi is really such an enormous deal, and here's why:
Most "car-guys" are like ADHD grade school boys. They buy/sell cars a lot. They get bored with the 986 and buy a 987.1. They decide they'd rather have a BMW for a bit, then move to a Mercedes SL. They go though their patriotic-phase and get a GT350. They get tired of that and trade for a 997. Their friends mock them so they buy a 992. They do this every 2 to 4 years and lose $10k- $20k every time they do. Why would I care if I need a new engine after 5 to 10 years of driving a car I'm going to keep? I'm STILL money ahead as compared to Mr. ADHD, and the process of an engine build can be a lot of fun. People wonder what's the matter with me and the musical engines I play with my car. I LIKE the mechanical process, and am always thinking of ways to improve it - this one's a rip-snorting firebrand, that one's a happy cruiser. I've been on a quest to find the sweet creamy center, which is probably not possible with a T1 - but it's been fun trying.
I like teh stock transaxle gearing with a .93 4th and a 3.44. It's not perfect, but it's as good as a guy can get with a 4-speed. I requires a ring and pinion that is generally NLA. Greg's long-legged gears replicate mine very closely with a custom mainshaft, a .82 fourth, and a 3.88 R/P. Almost everybody would like that for cruising or traveling on the highway.
What you want to do depends to a large extent on your expectations. Do you want to have a fun little car to zip around in for a year or two? Do you want to be the king of the mountain? Do you think you can be the boulevard bad-boy (you can't)?
... or are you the kind of guy who's a lifer - the guy who's still married to the girl-next-door, your high-school sweetheart, working the same job you started in back in your 20s. I'm not advocating for anything, but if your tendency is to make lemon-aid, rather than to go to the green-grocer to buy an orange, you can make the car into what you want it to be. Nobody knows what that is but you, and you probably don't know yourself until you are underway.
Welcome to the madness.