I've had my 150PD Bora around the 'Ring although I haven't done any track days in her I'd like to think she's more than capable!
Suspension wise she's running Koni Yellows and Eibach Pro Springs which are from a N/A 1.8 Golf, helps to lower the front and back end a little more to aviod that raked look. This has affected handling though, as I believe the shocks are just that touch out of their stroke range - but it's nothing too major.
I've also fitted front and rear ARB's, again Eibachs. To be honest you could probably just fit the front ARB on a Bora - the boot section at the rear provides enough rigidity in the body anyway. Plus the rear axle on the MK4 platform works as a rear ARB as well. If you go for the hatchback model I would advise fitting the rear though.
Brakes, after taking the advice of some folk on here I went for Zimmerman drilled discs and Ferrodo DS2500 pads, with Motul RBF600 fluid for good measure. I did find about quater of the way round the ring I was getting a hard pedal on some corners which I think was down to poor cooling and me using the brakes more than I should 
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Tryes - These are one of the most important factors in my mind. I swear by Michelin Pilot Sport 2's.
Remap wise - Went for Revo switchable. Last RR measured her at 187bhp and 302 ft/lbs - which is very respectable for a 6 year old car with 110k on the clock!
As for a good base, it all depends on what you want to spend. You will get a cheaper base car if you buy a Bora. As someone said on here recently, it's the thinking mans Golf 
Expect to pay £800-1000 less for a comparitvely spec'd Bora compared to its Golf counterpart.
The different power variations are mostly just engine related. All six speeds use the same ratios i.e. 115bhp, 130bhp and the 150bhp PD models. Out of those three the 130PD is the weapon of choice.
One word of warning. If you remap a high miler you will probably have to do the clutch at some point. All that torque is just too much for the stock clutch to handle. I uprated mine with a Sachs race pressure plate but kept with OEM parts for the rest of the clutch replacement. Budget about £700+ unless you can do the work yourself.