I am not an expert, but play one on television.
I sold my 50+ year old home last year. I had similar issues 25 years ago.
If you are in a municipality, you can talk with the building inspection office there and ask what their requirements are.
If you're like me and live in the county where there are no inspections and are just wanting to have safe wiring, this is what I did on my old home.
I installed a 200 amp service panel and then fed the old panel as a sub-panel. This allowed me to add new circuits, where needed and basically left the other wiring untouched. There are numerous ways to attack the ungrounded plug issue, but I've noticed that most of these are usually just used for lamps and other 2-pronged ungrounded appliances.
If, however, you have such plugs in the bath, kitchen and garage, it's time to think of upgrading. I would highly recommend running new grounded circuits to these areas. The kitchen and bath require a GFCI by code anyway. You will also need grounded plugs for the washing machine, disposal etc. as well.
As for number of circuits. The key word here is LOAD. Count up the number of WATTS that could potentially be used on a given circuit. Divide this by the voltage and it will give you the amperage for that circuit. This is a good way determine whether or not to go #14 cable and a 15 AMP breaker or #12 cable and a 20 AMP breaker. If load exceeds the AMP rating for that circuit...time for another circuit.
This is what I would put on dedicated 110v circuits:
3. Washing Machine
4. Garbage Disposal
5. Bathroom Heater/Vent
6. Kitchen Counter (GFCI)
7. Flat-Screen TV/High Priced Electronics - a dedicated circuit here can cut down, but not eliminate EMF interference. You need surge protection here as well.
8. Small Window Air Conditioner
9. 20 AMP circuit for the garage
220 v circuits:
1. Electric Range (unless of course you have gas)
2. Hot Water Heater (unless of course you have gas)
3. Central Heat and Air (unless you have a furnace)
4. Large Window Air Conditioners
You would also need 2 spaces for breaker that feeds the existing panel.
As you can see, with today's luxuries and appliances, it's easy to fill up a box. So, if you feel safe with the old wiring, check with the local inspection office. They may just allow you to sew a new patch on to old cloth. Otherwise, bite the bullet and rewire.