[The HACK]

1) Yes. It's because it's a shorter moment of inertia to overcome. Wheelbase on the MZ4 is significantly shorter than the E46 (and by that extension, even more so compared to the E9x) How do I deal with it?

Learn to anticipate the rear end coming around. Assume that it's going to rotate at every slow corner and whenever you drop the hammer. Correct the rotation before it happens.

2) Maintenance, yes. It uses mostly the same parts that an E46 M3 would use, for brakes, tires, oil and whatnot. Potential for upgrade? All but the lowest ends (like Megan and off-brand Taiwanese stuff) on the suspension side, and anything involving engine tune (FI, tunes, etc) are not available to the MZ4, at least not to the same extent as it was on the E46 M3. The S54 on the MZ4 uses a newer, more power ECU (similar to the E9x M3), therefore any tune designed for the S54 on the E46 won't work, and by that extension, any FI application designed for the S54 won't work without custom tune.

3) Stock for stock, or same equipment, MZ4. By a WIDE margin.

4) My philosophy is, if you can't go fast with 300 HP, having more won't help you. Heck if you can't go fast with 200 HP, having 300 HP won't help you. Keep in mind the MZ4 Coupe is around 250lbs lighter. For acceleration purposes, it's roughly the equivalent of 25 more HP than the E46 M3.

The problem, of course, is if you're even 1/10th of a second slower in applying your throttle upon the exit of a turn, that extra "25 HP" or 250lbs less won't help you much.

Where the HP and torque helps you the most, is in passing IMO.

I once got stuck behind Satch Carlson of Roundel at a local track day, he in his wife's Dinan 335i, I in my MZ4 Coupe. He would give me a point-by, then FLOOR the car on the straights. I went through half a dozen lap trying to pass him without breaking the rules of the organization we're with to no avail (BMW CCA. Passing with a point only is strictly enforced, and we're forbidden from passing into the braking zone).

Let's just say that was the ONLY time I ever wished I had more HP.

5) I'm just going to come out and say it. If your goal is to sell the 335is and buy 2 cars, you won't be able to afford a decent MZ4 Coupe. They EASILY command $8,000-12,000 more for equivalent mileage/quality E46 M3s. You probably will barely be able to do a straight-up swap with the 335is, much less buy an MZ4 Coupe AND an AWD/4WD beater.

If I were in your shoes? I'd get an '09+ WRX and put the rest into suspension and and extra set of wheels/tires or two. I had an '09 Wagon and with a set of Hoosier R6es, it could chase down J-Prepared E36s on track. Hoosiers AND suspension? It'll probably be faster than I-Prepared cars. You can track the WRX to your hearts content, and it'll be very comfortable for daily drive, especially in the winter.