hat - you are starting to move out of the normal realm of tapers, who most often have no access to on-stage micing, to the potentailly much higher quality of exacting mic placement which most pros utilize. i do chamber music where i always have access to the stage, and the ability to setup mics wherever i need them to acheive the best capture, since i am working for the musicians.
tlm170s are wonderful mics, and you should be able to do serious work with them. they are mostly studio orented mics (being LDCs), and most folks tend to prefer higher end SDCs for on-stage micing, due to smaller visual intrusion, better transient response, and smoother off-axis response.
i dont really know how much you already know, but in general, a basic ORTF setup will work for almost anything, and i would recommend it 90-95% of the time. using them as a spaced pair of omnis can work if the hall sound fabulous and you can place the mics close enough not to overwhelm the mix with ambience - this is often only 4-6 feet out from the performers, and i do not use it often in live setups. blumlein can be a perfect choice when you have a medium ambience acoustic and want to retain precise image placement, like a string quartet or small folk group. if the hall is too live or too dead, go right back to ORTF.
key to any of this is learning to hear reverb. until you are very experienced in assessing room ambience and how it will translate in a mix, stick to ORTF and learn to craft reverb during post - it is way better to get a recording that is too dry than one which is too wet. get ahold of the most expensive reverb hardware or software you can afford and really spend a lot of time learning to use it. altiverb is a good place to start if ITB. bricasti m7 is the heavenly hardware, though muy spendy. also keep in mind what kind of music you are recording - while a lex pcm91 can be perfect for vocals in a rock mix, it is often not the best choice for a oboe/piano duo, etc. normally, small acoustic groups will sound better with a large room algorithm than with a large hall setting.
all that said, you may want to visit the remote forum on gearslutz - lots of very knowledgeable folks hang there that do pro live recordings. you may also want to pick up a copy of john eargle's "the microphone book" - eargle was the premiere engineer for delos, and a design engineer for JBL, and that book pretty much covers everything you want to know.