Thanks for posting 

Name: TR_Karolus_Showcase
Clean: No. Dirties two references. Please clean with TESAME.
Lighting: Fog should not be set to 0
Northmarker: Present 
Fits exterior: Almost. building 7 can have a  3x2 top floor. You are currently 1 square short of reaching showcase requirement.
Pathgrid: You lack a pathgrid in the rear storage area
Illegal to Sleep Here: Yes. Correct.
Gridsnap: fine

A few further bits before I review thoroughly for bleeders/floaters/item choice etc

- You have some caspers where you have joined room and hall pieces together. For example, in the rear storage room you use a room corner piece when you should use a hall end piece.
- Greenlighting: for example, the candle in the rear room casts a green glow onto the table. This is greenlighting. Avoid this by using a lower radius candle (or moving it).
- A range of items lack X or Y rotation on the wonky furniture, correct this because otherwise they are bleeding/floating.
- The interior could do with slightly more clutter. Look at Narsis/Hlan Oek interiors for reference.

Name: TR_Karolus_Showcase
Clean: yes
Lighting: please brighten fog a bit 
Northmarker: present
Fits exterior: yes
Pathgrid: Duplicate node upstairs breaks connection. Path in storage area collides with barrel.
Illegal to Sleep Here: yes, correct
Gridsnap: yes

Bleeders:
p_vintagecomberrybrandy1
bk_RealBarenziah1
barrel_01_cheapfood5
de_p_chest_02_hpotions (also not suitable for this interior)
De_P_Table_01
food_kwama_egg_01
misc_de_foldedcloth00
furn_de_tapestry_01; furn_de_tapestry_04 - rope shouldn't bleed into the plaster
furn_de_p_bench_03
furn_de_p_shelf_02 - bled too much

Floaters:
Potion_Cyro_Whiskey_01
BookSkill_Speechcraft1
bookskill_security2
bk_BriefHistoryEmpire2
com_sack_02 - needs to be bled into the ground slightly 
food_kwama_egg_01
misc_com_wood_cup_01 - needs only slight adjustment
Misc_Inkwell - likewise
misc_com_broom_01 - handle needs to rest against wall, brushend should bleed slightly 
misc_de_tankard_01
T_De_HackloPipe_01
T_De_BookendPoor_01
furn_de_p_chair_02

Other: 
- T_De_FurnP_Bookshelf_01, use the vanilla de_p variant in a showcase
- Upstairs door should use in_hlaalu_doorjamb_load
- unnecessary in_hlaalu_room_post downstairs
- upstairs bookshelf needs more of a mix of clutter. eg some ornamental bowls etc. 
- book selection needs to be adjusted (too many skillbooks, books of same series, all placed laying on side), please see: https://wiki.project-tamriel.com/wiki/Interior_Guidelines#Books
- cut the pillow on the floor, and adjust the placement of the bed-pillow
- change the blueware pitcher to a more class appropriate variant 
- add some cutlery to the upstairs table
- attach the lantern to a rope, use one upstairs too
- either use the stair variant that has walls at the top, or add some guarskins around the stairs upstairs so its not a falls hazard
- de_p_closet_02 change to filled variant 
- unnecessary hlaalu wall behind stairs

Name: TR_Karolus_Showcase
Clean: yes
Lighting: fine
Northmarker: present
Fits exterior: yes
Pathgrid: Duplicate node upstairs breaks connection. Path in storage area collides with barrel.
Illegal to Sleep Here: yes, correct
Gridsnap: yes

Bleeders:
active_de_p_bed_04
bk_MysteriousAkavir
bk_OnMorrowind
De_P_Table_01
misc_com_broom_01 - handle bleeds into wall. broom end still needs to be bled slightly.
T_De_BookendPoor_01
misc_com_redware_platter
furn_de_tapestry_04; furn_de_tapestry_01 - wood should be stuck in the plaster, rope shouldn't bleed into plaster 
furn_de_p_stool_02 into rug

Floaters:
BookSkill_Speechcraft1
bk_AedraAndDaedra
food_kwama_egg_01 needs tilting 
light_de_lantern_03_64 - should be at bottom of rope and top of metal ring should meet rope 
misc_de_pot_blue_01
misc_de_tankard_01
T_De_HackloPipe_01 - handle floating a bit
misc_de_pot_green_01
misc_com_wood_knife - should be tilted so the handle lays flat 
misc_com_wood_spoon_01 - as above
furn_de_p_chair_02

Other: 
Misc_Com_Pitcher_Metal_01 - for a dunmer int typically better to use a de_ pitcher like red or stoneware
 

Bleeders:
tapestries still bleeding into wood
furn_de_p_chair_02

Floaters:
bk_OnMorrowind - needs to rest against book
misc_com_broom_01 - needs to rest against wall
bk_AedraAndDaedra - needs tilting
food_kwama_egg_01 - needs tilting 
T_De_HackloPipe_01 - bowl is slightly floating
misc_de_pot_green_01 - floating 
misc_com_wood_spoon_01 - spoon head is floating 
 

Bleeders:
misc_com_broom_01 - into the wall
food_kwama_egg_01 - into shelf

Floaters:
bk_OnMorrowind - still has a gap
bk_AedraAndDaedra 
T_De_HackloPipe_01 - bowl still floating 
 

DM'd new criteria