Yes, the problem is that I have not much experience working with metal, and this is my first go kart, and I dont know if I am will be able to do all the suspension stuff.
Don't want to discourage you, just want to give advise from experience.
Those tubes are 14 ga steel, which is about .078 thick, which is about a penny and 5 pcs of note book paper thick (.062 + .015) not the easiest to weld with a cheap 110v flux core welder or cheap 220V tombstone stick welder.
Do you have a welder?
I notice the suspension one has a fully welded frame except for the floor pan
I see you mention suspension, so I looked at the suspension one, for me the cons are:
It will take at least a $1000 dollars to finish it up I believe or more
an engine, 4 coil overs, axle kit, brakes, steering wheel, heim joints (rod ends), steering shaft with bearings, seat, spindles ,wheels and tires etc... not to mention you will have to fabricate all linkage for steering, brakes and gas
Also that rear suspension is not really suspension in the way you
might think, the axle assy., brakes, tires, wheels, engine, torque convertor etc is a lot of wt. to move, the frame
will break at the two mounts especially if it is rode hard.
The front suspension is not made for fast rocks/bumps and jumps that put pressure rearward, it is made for yards with maybe 2" dips.
Just welding a 3/16 x 3 inch x ~24in plate between the rear uprights and lower 1x1 would of stiffened and spread the load when the1/4 in mounts are welded to that. , with all 6 surfaces welded to it, now they are welded to a thin 1x1 tube and the rotational forces will not be happy
Again, not bashing I just don't think this will make you happy, after making a parts list and studying how much work you will have to do to it.
Make an excel spread sheet and input just the parts I mentioned to see where you sit.
You'll also need a grinder with wheels, drill and drill bits, possibly taps for steering linkage