Because it came up, I have to put this here

lease keep in mind this is about IMTU.
Jump Space IMTU
Jump Space works as per the article in JTAS 24.
Jump field drives, Jump plate using drives and Jump Grid using drives are all in play. The differences between the three are mostly cosmetic, dealing with the size of Jump Envelope they create, and what that entails. Jump Drives that use Plates or Grids can operate in Jump Field Mode if they have to (usually done when there has been damage to the hull and you need to Jump).
Hydrogen is not needed for the Jump Envelope, A powerplant and a functioning J Drive are. (It's a field not a Hydrogen Bubble!).
The Hydrogen used for Jump Fuel is burned by the Fusion PP to Power the J Drive when it tears opens and closes the Hole into Jump space. The power to rip open and close a holes in reality is immense, and requires overclocking of the Fusion Power Plant to get this power fast enough. Thus, the fuel requirements for Jump
using Fusion Power Plants. In jump space the J Drive doesn't need more power than is available from the Fusion Power Plants regular operations to maintain the jump envelope. Exiting Jump Space doesn't take immense power, its a natural process that occurs at the end of your time in jump.
Turning off the J Drive while in Jump Space is Bad. It can kill everyone on board over the course of a few hours, and it is an IMMENSELY painful and sanity warping way to go. ("Ship arrives with crew and passengers Dead!" is an occasional News Headline IMTU). It's a nasty and visible form of miss jump.
Gravity Wells that can effect Jump HAVE to be large NATURAL gravity sources (> 1 000 000 Dtons) until TL 21 when the Jump Damper and Jump Projector are invented. This does mean you can initiate Jump from inside of a larger ship. This is a bad idea, as anything inside your Jump Envelope, the size of which depends on if your running a Jump Field Drive, Jump Plates or Jump Grid, goes into jump with you. This can do severe damage to the ship your Jumping from, and if enough mass is taken with you, you can expect not only a misjump, but damage to your ship as well (possibly catastrophic). Jumping out of a ship that is already in Jump Space is always catastrophic for you, sometimes for both ships.
Drop Tanks and Jump capable small craft do exist IMTU. Drop Tanks, when used, can not be used with Jump Field Drives, or with other drives running Jump Field Mode. Drop Tanks use on ships using Jump Plates run an increased chance of mis-jump. Ships using Jump Grids can use Drop Tanks without any problems.
I think that between the article, and my notes here, that covers everything.