Sorry to tell you this, but designing or engineering a system is probably better left up to professionals if you, basically, have no idea how an inverter works.
An inverter basically takes a DC and (for simplicity) chops it up into little bits. It then it takes those little pieces and (through some waveform processing) amplifies the voltage and reassembles the waveform to look like AC at a certain voltage. The output waveform then is considered AC. If you are talking about a cheapo inverter, it probably is modified sine wave output, and this is the least favorable waveform, but for all practical purposes, will usually work fine for most resistive loads and a few others. These will not be able to grid tie.
The next step up in waveform quality, is a true sine wave inverter. These are usually more expensive, and will power most loads fine. For a battery based sine wave inverter, the only thing you have to worry about is the start up current of inductive loads. You have to make sure your inverter and wiring is sized appropriately.
Battery based inverters work with low voltage DC and invert it to high voltage AC at a lower current. These are usually less efficient that grid tied inverters in two ways.
First, the overall voltage differential is greater, so there is more internal transformer loss during the conversion process.
Second, you have the battery efficiency to deal with, so the power put in by the PV, will always be less than the inverter output because of the losses inherent with the chemical storage medium.
Grid tie inverters work most efficiently. The DC on the input is usually kept higher than the output voltage. This creates less of a differential, and therefore an easier conversion by means of switching power supplies which have higher conversion efficiencies because the current is kept to a minimum. If you understand ohms law and the fact that voltage and current are inversely proportional, this will make sense.
A grid tie inverter will feed your service panel in parallel. It will sync its frequency and voltage to the utility standard and back feed your service panel in a way that attempts to raise the voltage slightly. If it can do this, then the current will rise and it will push power back onto the grid to then be sold to your neighbors at the retail rate, unless of course you are using power in your own home that is of greater wattage than the inverter is providing. Then the power would be used in your own home. This is all done automatically.
You do not have to have a battery bank hooked up to use a grid tie inverter, BUT they do make versions of grid tie inverters that have battery back up. They also are usually slightly less efficient however, but if you need the backup, then you have to deal with it.
You can certainly buy 1000w of PV and hook it up to a 2000w inverter. This will allow you some room to add on to the system in the future. HOWEVER, you need to make sure that the PV strings are sized appropriately for the inverter you decide to use (they are all different). There are MANY different PV modules also, and you need to select your components properly also or you could be very disappointed in the performance of the system. Make sure the service panel can handle the increased current that might be provided by the inverter and that your panel buss bars are sized appropriately.
All of these things I mentioned (among many others) will probably be covered by the contractor the utility company has referred you to. If it is done professionally, it usually isnt cheap.
