you do not state how much experience you have with Tig Welding so if some of my answers to your Questions seem to simplified it is just that i want to try to give you a feel for the different units.

From reading your requirements then i would have to say any model AC DC Tig we have will be apropriate for your needs . The question then remains what is the best for you.
you can get carried away and look at some future Models that are complex in Setting and require a more advanced knowledge in setting the machine to get the correct welding parameters etc.
Or you can go to the basic PowerTig 185 Micro with a simple Frequency and balance adjustment for AC and no other adjustable settings besides amps and post flow . this is probably the easiest set up and use Welder we have for AC /DC .
my own recomendation would be to go with either the 200DX or the 225LX with the edge going to the 225lx because it has a few other settings and i prefer the foot control set up on this over the 200DX.
Setting aside the foot pedal ( it is not a big deal but you have to set max amps on the pedal ) the 200DX is probably all you will ever need and the settings are practical and not exotic and of course you have the pulse features which is particularly handy for Stainless.

One last point i should bring up in regards to the 185 is that this past December we did a few changes to the top board and this was done to improve reliability and protection to some key components. in testing them at the Factory i was very pleased with them and then again here in Canada ( today actually ) i was going over them and i am very pleased with them.
One point that may be of interest or even a deciding factor is the new Amp Control Tig torches will fit the 200dx 225lx 250ex pp 205 and pp256
cheers
Duncan