The Beta 58 is a good vocal mic, could probably double fairly well as a Guitar Mic, mostly used on stage, wont be used completly in a studio setting though, in fact rarely will be. That being said though, both the 58a and 57 CAN be used in a studio, and are good cheap starter mics. If you are trying to take sound from an acoustic at the same time as vocals are they both from the same person, as in are you playing the guitar and singing at the same time, or is someone else playing and a different person singing? Really are you recording one or two performers? The reason I ask is even with directional mics from the same performer you will probably get some bleedthrough, and it would be better to track that, but with different performers and a couple of cardioid you can limit it rather well and get useable stuff at the same time. But that is mics and you were asking about hardware and software. But keep in mind obviously if you want to pull audio from two sources at the same time, you will need two mics and since you know what your sources will be you can customize your mic selection to fit it better.
Software Cubase supports plugins, VST most specificly which there are a lot of them out there, so you wouldnt have problems with expanding plugins later on by any stretch of the imagination. In fact most decent audio programs support some form of plugin, if they dont, I owuldnt waste my money
Even the Open Source software has the LADSPA plugs they support to give you some flexibility. Just be careful as to what type of plugin you get and make sure it is supported by your sequencing software, there are many different types, VST, AU, LADSPA etc. Most support VST, But several also have a proprietary format they support as well so not all play well.
Cheap software by the way does not equal bad. I have used CuBase,Nuendo,ProTools, and many other programs, but what I use the most and like the most for straight audio work is a free program for linux(Which is my OS) called ardour. Admitedly though in the case of audio finding good quality programs can be tough for not much money.
And here are a few of the threads on various topics that may or may not interest you.http://notebookforums.com/showthread.php?t=72824http://notebookforums.com/showthread.php?t=69136http://notebookforums.com/showthread.php?t=70020http://notebookforums.com/showthread.php?t=69195http://notebookforums.com/showthread.php?t=67625
Have fun, post back with questions and comments.