Hi Ed,
There is better people on here to give you advice but here is what I can offer;
firstly you will need an interface, a simple one if that is what your budget offers, either usb or firewire. Youll Need one that has a line input for your guitar and and midi ports also to hook up your keyboard. One of the most cost effective interface is the edirol ua4fx which I have used solidly so far,has basically everything to get you started ~(including some guitar effects), although only one source can be recorded at a time as you have stated,you will be surprised after a while how you will start looking for more inputs/outputs! so get what your budget will stretch to.
in relation to software, Ive only ordered x1producer and havnt tried it out yet (been using home studio 6, which has everything except some high end polishing tools) so others here will tell you how the essential version works,either way it will have the tools you need,but there will be weeks of learning involved (be prepared for that!
Computer, for what you say you want to do then a laptop will suffice, although the new specs for sonar x1 recommend minimum dual core 2.4 ghz which I would suggest you look for whether it laptop or desktop. most stock computers should have a good deal of ram packaged with them now to suffice,but if its a cheap option to upgrade to more,then you wont regret it.
What you are looking to record (i.e a few midi/audio tracks) would not require too much power. But the most important equipment is your interface/soundcard, everyone will tell you that.
Cian
post edited by whack - 2011/06/04 08:16:51