I'm mostly just concerned about not being inadvertently over exposed to, say, Japan and making sure that my portfolio is not missing anything fairly standard, like small caps.
Basically I want global equity trackers, with property, and just want some input from experienced people here to help me find a reasonable allocation to each
Not to sound like a broken record, but only *you* can decide whether you want to be more exposed to, say, China and less exposed to the United States. Everyone has their own ideas about what overexposed or underexposed means going forward. Whether you like the historical stability of the US market going forward or think that our future is bound to collapse is a personal call. Likewise, whether emerging markets will (e.g. Brazil) will become a major global player or suffer from corruption/war/poverty is any analyst's guess.
But - I understand how daunting a task it can be, so I"ll tell you what I have done, and why. Note this is specific to ME and your reasons will certainly be different.
70% in VFIAX (SP500 fund)
20% in VTIAX (International large-blend fund)
10% in VISGX (Small-Cap growth US fund)
First, I personally like a dirt-simple investment strategy. Part of that's because I think being very simplistic can yield returns that are good enough for my purposes, and part of that is because I think many people make asset allocations that are so complicated they psych themsevles out.
Why VFIAX: The SP500 are the 500 largest companies traded on the US stock exchange. However, 1/3 of all the profits from SP500 companies come from abroad, so you do get some exposure to international markets there. I like that the US is a world-reserve currency, I like the historical data for the SP500, and I like that, for all its problems, it's a pretty straightforward marketplace unlike, say, Russia.
Why VTIAX: In short, I wanted to increase my international exposure, but own mostly large established companies. Yes, I loose out on some of the tremendous growth of smaller international companies... but I'm ok with that, mostly because I think the volatility of the larger companies will compensate for it.
Why VISGX: I added this component recently, and it gives me more exposure to the growth of smaller companies. So now I own mostly large US and International corporations, as well as a small chunk of small US companies.
YOU might want a completely different allocation. I don't have any bond exposure, nor am I buying precious metals or small-cap companies in regions like Africa. I also have relatively small international exposure (though see the comment about 1/3 of all profits from SP500 coming internationally), and what exposure I do have is largely concentrated among large-cap international companies (Toyota, Nestle, Samsung etc). I'm heavily weighted on US stocks - which is exactly what I want. I don't have any mid-cap exposure either. I could add some, but I like my simple approach the way it is. Others would want more diversity.
ALL of these various things may matter to investors in a different way.
G'luck.
