You can buy Imbel Manor before joining the Thieves Guild, in which case Armand will not let you in, or after killing Jak.
The price is 60,000 and the upgrades a little more. It has two more beds than the normal layout (which was mostly retained). The extra beds are added in the dome, and the second room of the servants quarters. Some of the open space downstairs is used to hold display cases and bookcases for the collector. The center section of the basemant that used to have the entrance to the catacombs is now a workshop, and can be purchased with custom content for Mage, Fighter or Thief.
To allow the Boots of Sprinheel Jak to be obtained without doing the TG questline, I added a small quest that takes you into the catacombs through a new section of sewers, so you can slay the vampires there, including a clone of Jak himself. This starts after you have purchased all the upgrades.
http://oblivion.nexusmods.com/mods/42764
The only mod I know that may conflict with this is http://oblivion.nexusmods.com/mods/29333 which puts new homeowners in "released" property. Ones affecting the TG questline may force you to take the "after Jak dies" option.