Ok, I haven't touched this project much since my classes begun this year, but since I have started it I had 2 ideias for this project that meet my goals in one way or another.

I have concluded that I can make the case 50% or even 40% of the original IBM 5150 case with enough space for the main board, a small power adapter and some expansion, maybe I have to use a external power adapter if things become messy (I hope to put everything I need inside the case for full out-of-the-box functionallity), but I think the expansion is going to be a major problem, since it needs to have the same expansion capability but with restricted space. Of course that any ideas and suggestion are welcome. 

My major ideas for this project are: 

1st idea: Use the same board design as the Sergey's Micro XT (Use a backplane)

I was thinking about using a small backplane vertically mounted with the standard 8-bit ISA slots, it is the way that Sergey designed his board to be. Maybe reducing the spaces between slots.

Pros: 

-It is fully compatible with existing ISA boards

-I guess it is a bit less electrically noisier compared to those cheap pin headers

-I have significantly less work to do designing boards compared to the other idea (I kinda want to have some work, otherwise I would not have started this project, but not too much work, I'm still lazy)

Cons:

-The boards need to be smaller since the backplane occupies horizontal space, reducing the expansion options

-Those ISA slots are a bit more expensive and harder to find nowadays (not something i'm much worried about)

2nd idea: Use a more compact vertically stacked board design or 8-bit PC-104

I was thinking about using those very common pin headers that you can find in any electronics store, one on each side of the board. These connectors doesn't always give the best electrical connection but I think it does the job. In this case there would have more space available for the boards but the pins in existing designs would have to be rearranged for this new pinout or an ISA adapter would need to be used.

The PC-104 option (used in many compact and industrial applications) is kind of a mid-term option, it uses a compatible and standard pinout, allowing existing boards to be plugged in (The information I found says that it is usually 10cmx10cm wide, so I could stick to 40% the original size). Probably this is the best option for what I want.

Pros:

-Cheaper connectors (I think that everyone knows that college students are not particularly rich hahahah)

-Common parts

-More flexibility in the design sizes, complexity, etc., since I would have the freedom to arrange the pins however I want and would not be restricted to sizes

-PC-104 design: Compatible with existing boards (significantly less boards than the usual 8-bit ISA in home PCs)

Cons:

-Electrically noisier, less stable computer

-Not compatible with existing boards

-A bit more work to be done

-PC-104 boards were used in more specialized applications, so it has a less variety of existing designs especially for XT class PCs (something that could be solved designing new boards or making an ISA adapter would be possible i guess)