They had a rather lovelly pullout of it in one of the Startrek Fact-Files of it. A quick look on the Ex Astris Scientia site found it here -
http://www.ex-astris-scientia.org/sc...eet_ships2.htm
but as thery say very little is known about it, though in the picture you can clearly see it towing a much larger craft. Details all on the site, under 'tug'.
Generally I quite like your helm manouver idea. The only thing I find missing is any sense of scale.. I.e. A Federation tractor beam is not as powerful as a Borg tractor Beam.. It's not totally neccessary, but it's just a thought.
Yes and for orbital decay in atmosphere - read plummet! Actually they would need orbital correctors in the sense of weather systems. I am reminded of super large tankers which have stabilisation systems to cope with tidal swell. You would need adjustment engines to combat violent storms. Something like the Suliban Helix would need a really robust stabilisation system. I recal seeing a documentary about weather on other planets, and as a comparison the winds in Jupiters atmosphere could reach ten times that on earth.. not nice weather to fly in! ;-) Although rare a couple of nods to fluid based manouvers might be nice. I'm thinking particularly of the Ocean world episode in Voyager. Lower atmospheres of Gas Giants are also fluids though also extremelly high in pressure and generally deadly (as covered)
Something else I have thought you could add would be a Phasing cloak and associated rules to it's use. While it's generally illegal and extremelly unreliable in the federation, we have seen two species using it. Namelly the Voth and those aliens who performed all of those rather nasty experiments on Voyagers crew while slightly out of phase. (apologies if it's already been covered. I do miss some things.)
One handy thing about netbooks is you don't have to print errata - only release new versions ! ;-)