In answer to your first question...
It is far harder to find timber desireable TPI's than it is healthy steel. With enough heel you can always have a new set of teeth cut, but modern machines/s-svcs cut in a strait line and the absence of that belly does diminish efficiency.
3 TPI is the Holy Grail for rips - uncommon and expect to pay accordingly - look for 4's don't pass up a good 5
3 1/2 - 4 1/2 is your target for crosscuts, most in this catagory were marketed as "docking saws" to sawmills to buck/dock stock to length quickly, these often have metal handles and are 30" as oppossed to the more common 28's & 26's - again don't pass up a good 5
I'll answer your second question with another question - Is this a Bic/disposable version ?
