Marc/Avery:
MTU is fairly closely CT canonical, with a few exceptions. I use the MT rules (and now the T4 psionics rules), with decorations and contacts grafted into basic CG. I don't allow Advanced generated characters, as a general rule. (If there had been an Advanced for every basic, I would have made all CG advanced).
I typically set between 1085 and 1115, but sometimes go throuugh about 1150; I NEVER AGAIN will use virus; IMTU, the hard times hit, and the 3I rebuids from Dulinor finally finishing the job on Lucan, and the "Real Strephon" (IMTU he is the Real one) bowing to superior firepower, and formally abdicating in favor of Dulinor once Dulinor finally (ca 1130) gets Lucan, and takes the capital by force, calling the moot, and then Strephon shows and abdicates in favor of Dulinor.
Nobles IMTU seem slightly more involved, and IMTU the 3I tends to overreact when it finally notices violations of the Imperial Laws... Imperial marine Battlegroups landing a brigade of Battledress, and 2 or 3 of armor, plus another brigade of leg in Combat Armor, are not uncommon. Meson fire on holed up leaders also not unheard of.
I do use the DGP materials. Extensively. I don't limit to 7 terms, I don't use Int + Edu, I allow multiple careers (subsequent enlistments at -2 DM per previous service unless single term draftee; GC ends by choice or upon second forced out). I have a variant on nobility, including several grades of knighthood, and make it possible for Reward nobles to have fiefs (in lieu of higher courtesy ranks). I use (Terms * Cr2000)+ (Officer Rank * 1000) for retirement pay; Enlisted rank has a automatic E2 by end of 1st term, and further promotions 50% shot per term 1d: 1-3 no, 4-5 1 rank, 6 1 rank, plus second rank if MCG or SEH. I use the six rank system of Basic CG, and a 9 rank system for enlisted (where appropriate). I allow rank-less careers an additional bonus skills off special duty (1 at SD TN, 2 at TN+4, 3 at TN+8, and one extra for Natural 12).
I use a slightly modified HG (match the Jump Drive fuel formmula to MT's) for big ships and insignificant ships. For PC ships, I use MT Craft Design rules.
Many (but by no means most) worlds have their own local currencies; almost all megacorps have corp-script. Corporations earn their LIC by donating 5% of their stock issues to the Immperial Family. LDC (Domain LIC's) go to the archduke, and the Archduke is expected to pass on a 1/5th (1% of total issue), LSC's (Sector wide LIC's) are 5% to the sector duke, but he passes 1/5th each to the Archduke and the Emperor), and LLC (Limited Liability Local Charters, the Subsector equivalent of an LIC) are sent up the chain frm the SubSector Count or Duke. World Imperial Nobles are typically enfeofed with the starport, and make their moneys fromm administration of the port; they are also the de facto Imperial Consul for the world; major ones may have a formal conulate system. Where the local government has a noble in charge, he is usually also regonized as an imperial noble, landed and such, but with nigh-auto approval of candidates to take office. Imperial Feudalism is Fealty to both immediate governance and the emperor. Sector Dukes run the Sector Government, Subsector Dukes or Counts run the Subsector Government. Some minor polities have succesfully lobbied to get counts or marquis who have a see in a less-than-subsector imperial sub-government; they typically pay token service to the subsector count(s)/duke(s), from whomm they are responsible. Almost all imperial members maintain a local navy (even if it's just 2 G-carriers and a dozen inspectors), the Subsector and Polity Governements have subsector navies, and the Sector Government has the Reserve Fleet; the Imperial Main Fleets are run by the Domain Grand Admirals (who, since the reinstatement of Archdukes, now have to answer to a local noble's oversight and budgeting, rather than the far-off emperor). There is no standing Imperial army, coacc, nor sailors; there is a standing imperial navy, marine, and scout service. There is a standing Planetary Forces Command at the imperial level, drawn from world and polity armies. Subsectors may have a small standing army, and sectors and domains may maintain a reaction force, but these are properly Huscarles units. Sector and Subsector dukes may hhave units comprised of Imperial Marines. Mercenaries and Starmercs have to be licenced; The Pirate career is really the Starmercs.
I make a distinction between citizens of the imperium and subjects; except for barbarian, all the PC careers enable one to obtain imperial citizenship (I assume PC's have done so, unless they state otherwise).
As an aside, I use a palmtop computer for die-rolling in almost all my gaming; PalmOS utilities would be a good thing for any new ed...)
IMTU, there are some other things which are best left undefined in canon: Norris and Branj are lovers; Lucan shot Varian (and Dulinor's men had video), Most of the moot acknowledges the Right Ascension by Personal Assassination. The Solomani run under "White Man's Burden" racism rather than "Deep South Postbellum/Jim Crow" racism. Interspecies marriages are not seen as a problem by the Imperium, nor are same sex; it's simply a matter of making the marriage legal on ANY SINGLE member world... but there are varying social ramifications.
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-aramis
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