Planning to buy a Nissan Cefiro A31 to be used as a daily car and a weekend fun (gala, porma, show/dress-up, drift) car.

1. Which would be a better choice? A bone-stock A31 or decently modified A31? Why?

2. Stock vs modified, pros and cons?

3. SR20DET vs RB20DET vs RB25DET?
a. Any inputs regarding each engine's fuel consumption?
b. Which would be better, fuel efficiency and power-wise?
c. Any ideas how much would each engine swap costs?
d. Which is cheaper to maintain?
e. Which is easier to modify or upgrade?

4. Any inputs regarding RB24S' fuel consumption? (In-case I'm buying stock)

5. Is it a "must" to seam-weld and align its chassis? What are the advantages? How much would it cost?

6. Any other suggestions?

Just another noob here. Thanks a lot for your inputs!