Rakuten iDeCo - Fund Allocation Help

[Bushiman]

Hello RetireJapan...
I don't know where I'd be without this site -the information is invaluable. Thank you.
I've read the RetireJapan iDeco guide, and just started The Millionaire Teacher to try and get a better (proper) understanding of my finances...

Anyway, I've just sent my application away to open a Rakuten iDeCo and am now trying to decide where/how my funds will be allocated...

I'm 37, a directly hired ALT at a JHS so my maximum monthly instalment is ¥12,000.
I'm thinking of breaking my portfolio into 70% Equity, 20% Bonds and 10% REITS. (Forgive any finance jargon mistakes, I seriously had no clue about any of this two weeks ago, and it's almost like learning a new language...)

Any advice or blaring mistakes, please help!

With the limited products available from Rakuten I've come up with this:

Portfolio:
42% 030 Rakuten · National Stock Index · Fund (VTI) for the US market (E.F. = 0.1696%)
14% 031 Rakuten · Worldwide Equity Index · Fund (VT) to give me some exposure to European/emerging markets (E.F. =0.2296%)
BUT, I've been reading (trying to understand) about triple taxation on this fund!? Is this correct? Japan won't tax me as it's in a tax-free iDeCo, no?
14% 003 Tawara no-load Nikkei 225 for the pure Domestic market (E.F. =0.1836%)

20% Tawara no-load advanced bond ticket for overseas bonds (E.F. = 0.1836%) from what I'm reading, domestic bonds aren't worth it...

10% Mitsui Sumitomo · DC Japan REIT Index Fund (E.F. = 0.2808%)

The whole triple taxation thing has me worried... Should it?
I'm wondering whether to switch out the Rakuten Worldwide Equity Index for:
011 Tawara no-load developed country stock (E.F. = 0.216%) as this is not a VT fund wrapped by a domestic company like Rakuten's offering (is it?)

Am I overcomplicating things? I want something I can set in motion, and leave mostly as is...
Should I just go with US, Domestic, Overseas Bonds instead?

I also read up on things like the Sharpe Ratio and Information Ratios...
Are they really worth looking at? I mean it really can't be as simple as:
Sharpe Ratio >1 is considered 'acceptable to good'. >2 is very good. >3 is excellent.
Information Ratio <0.4 is not a good investment. 0.4< I.R. <0.6 is good. Anything over 0.6 is excellent

As you can see, I'm new to this game, but willing to learn. Any comments or advice would be greatly appreciated...
Thanks for your time!