Nazi germany might have come up with most efficient way. Unprecedented how quickly they grew and easily managed to handle the affairs of the states they occupied. Somalia should become self sufficient in agriculture and textiles then print our own money
Inshallah but we'll need a different system for it. Posted an idea to implement it below. Just look for the break.
Your biggest foreign currency expense is importing knowledge.
Also these types of closed loop systems are inherently unstable because others could come in underprice you to take the pillars you've built your economy on.
This mainly because of the inefficiencies in your system.
The reason why we trade globally is to lower that inefficiency through specialization.
Look into comparative advantage trading.
These things you're thinking of has already been experimented with in the last century with not just Nazi Germany but also post colonial Africa and India.
It could help with quickly mobilizing a non productive population but it quickly loses steam after a while due to multiple reasons.
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I think we'll need some sort of hybrid system with possibly using more than one national currency.
Sounds crazy but it could be a solution to the drawbacks of the closed economy you're after.
Maybe a conventional Fiat currency initially pegged to the dollar and a public bond note as incentive for the population to participate in public works projects.
Help the government build farms, highways, factories etc and in return the government pays you in bond notes.
I.e. a standard bond issuance but instead of asking for money from the global debt markets the government trades it for time & skills of the population.
Then the government could pay for those bonds by taxing a more productive economy and paying out a decent yield.
Bond holders could then either hold on to those bonds & receive loan payments or sell them on the public market for the national currency.
100,000 Somalis donating just 10 hours a week on these public work projects could with proper management provide over 1.5-2.5 billion dollars a year of value per year ($20-$50/hr productivity value).
That probably would be the cheapest way for the government to finance development & train a labor force at the same time.
If the payout of the bond was at 10%, each person could probably make around $5/hr and the government would've made 10x that.
If just 10% of the population participated for 10 hours a week the government could implement 30 billion dollars worth of projects every year.
At most they'll spend a couple billions in importing knowledge and equipment we can't produce domestically.