So I have a few questions when it comes to planetary descriptions and coordinates...
1) What do you do with Arcturus, a real star that has coordinates in Hipparcos (or Henry-Draper, etc.) Catalog that puts it in a different location than the BT world. Is there an Arcturus (BT) and Arcturus (ACT)? Or shouldn't I worry about it at all?
Don't worry about it at all.
The main reason is that I am using a 3d mapping program to map out the Battletech universe. The planet as it stands is awesome, but almost two dimensional (I know... paper map and all). If I add real world star systems, then I get a huge sphere that shows possible systems where a jump could happen, but nothing exciting exists.
The BT star map is, and has always been, a 2d map. So when you put it into the 3d format and you get those big gaps you're seeing why they kept it 2d instead of 3d.
As for the big areas where nothing exciting exists, they were actually a plot point in several stories. Ships
can move through them, but since (A) they're abandoned systems and (B) JumpShips could suffer an engineering fatality at any time, usually ships don't move through them. I can only think of a few times it's happened in the fiction.
2) Is it possible to add a different culture (say based on HALO, but without the aliens) since the Clans are technically a different culture. They are human, but genetically better.
It's your game universe. Do whatever you like. CGL has dramatically cut back on the numbers of Game Rules Compliance Officers in their employ so you're free to do as you like.
Era Digest: Age of War has several smaller factions that existed before the Great Houses and were later subsumed into a House. Any of the
Handbook: House Whatever volumes has information on regional cultures in the Great Houses as well. I think
House Arano: The Aurigan Coalition is the latest one, and it might be a good model because it talks about a small Periphery nation that didn't exist before 3020.
For some really fun (almost goofy) examples, you may want to check out
Welcome to the Nebula California,
War of the Tripods!, and
Necromo Nightmare.
3) What do you do with the planets that are not in the "standard" Spectral Type? Sometimes the safe Jump point is given, but a lot of times it's not. I'm trying to figure out a standard way of telling where the safe jump point can be calculated. As in the Lagrange point or something like that. It would vary according to the luminosity of the star.
Just curious.
KSilvereyes
Rules for Hyperspace Travel are on pages 86-89 of
Strategic Operations and cover most of what you're asking. For a more human friendly approach to the topic that provides details, look at the "AEROSPACE TECHNOLOGIES" fiction that starts on page 122.
Page 134 has answers for the questions you're asking. Here's a quick quotation that you may find interesting.
JUMP POINTS
Where can you actually use a jump drive? Everyone’s heard that
JumpShips have to jump from and to “jump points,” but what are
jump points and where are they?
(snip)
... the points on the system’s
proximity limit intersected by the poles of the plane of the
ecliptic, which is the plane most of the planets are on. Generally,
these least-troubled jump points are “over the poles of the star,”
since stars tend to have an equator close to the plane of the
ecliptic...
Today, we call these the zenith and nadir points.
In fact, the zenith and nadir jump points are so preferred
that all other points are called “non-standard jump points,”
even their fellow proximity points.
The fiction is credited as a "Tharkad University lecture broadcast at the Lloyd Marik-Stanley Aerospace School. Used With Permission."
Far more detailed information re: stars is in
Campaign Operations "Solar System Generation" section, pp. 98-133. For example,
CampOps has the PRIMARY SOLAR STATS TABLE, which contains these data types: Spectral Class, Charge Time (hrs), Transit Time (days), Safe Jump Distance (km), Mass Mstar/Msun, Luminosity Lstar/Lsun, Radius Rstar/Rsun Temp (K), Lifetime (Million Years), Habitability Modifier.
Should give you everything you need. And NeonKnight created a
Solar System Creation EXCEL Spreadsheet which may or may not be useful for you.