[Modena]

Unfortunately the answer to your original question is, it depends on YOU, and not individual experiences.

People's responses here are largely driven by what they experienced, and largely this is irrelevant to you because everyone has a different skill level and experience. If one person said "it's really hard" it does not mean you will find it hard - same goes for the bloke who says "its pretty easy" - doesn't mean it will be easy for you, and for your skill set and experiences.

Perhaps try to think of it like this, forget that it's a Cobra for the moment; let's say you had a large garage area, and a fairly simple vehicle, say a HQ Holden, was completely disassembled and sitting in the garage area.

You have SOME level of instructions (amount varies by vendor).
You have most of the tools you will need, but you WILL need to buy some.

Would you be able to put the car together completely and finally, and safely drive it down the road?

If with full instructions, you could do this, then you can build a Pace.

One last thought, how hard do you want to make it? As you delve more into Cobra's will find that not only are no two alike, but they are all personalised. How personalised do you want to make this? You might not like the way a supplied wiring loom is designed, and choose to make your own. You might not like the sidepipes that a supplier might have, and choose to make your own.