Property and how many

Sole ownership B

Shared C

But as some have mentioned it is not the numbers but the returns you are getting.

I've written on this forum before an example of one portfolio that started with borrowing 2K in 86 to help buy the first property worth 75k to now having multiple properties worth over 2 million combined in value but debt of only 800k in 2006.

One key is to make sure the properties are CF+ enough to cover any unexpected costs like 2% interest hikes or no tenant for 2 months.  Second key is to look after your tenants as they will most likely look after you but then again I've also had the tenant from hell which I've also written a post about.  3rd key (just a personally favorite) which I consider to be very important is the LVR and I like to keep this at levels that can cope with a 10-30% drop in prices just in case the crunch comes and something needs to be sold. 

My investing style is purely buy and hold for long term growth.  May not get rich as quick as other methods but has certainly worked for me so far.