Will I be able to return to the Slums District to access my stash of items in the Copper Coronet Inn (or whatever it is named) )after I get Imoen back in my party? i have many items (Shortbow +2, Short Sword+2, spells,etc.) stored there for her.
Yes. All containers that are not degradable, ie. not pseudo-containers (loot/bodies, etc.), are permanent. Be warned, though, that leaving things lying around outside of containers is a certain way to lose them when the cells get reset. You can even store things in Watchers Keep containers in BG2 so that you can 'import' them into Throne of Bhaal.
One of my favourite spots for storing used quest items and sundry things is in the two table containers outside the Copper Coronet; for stuff I need to frequently access in BG1 (central location) inside Friendly Arm Inn and so on. They're safe.