No guide is waterproof as there are countless strategic options and you never know what your opponent does but if you go for a diversified army of 5 AT, 5 arty and 5 LT plus your starting troops you will at least stand a chance.
building one IC is a good strategy but then you don't have enough rares for knowledge. Infrastructure level 3 is faster build then Industrial complex level 5. I prefer to build an industrial complex only once my Infra is level 3 because both buildings do the same they produce 50% extra.
It is possible to build a lot of infra if you follow step one which is buy all goods and steel on the market that you can.
Hmm well the extra IC makes for quite a big possitive difference in unit production in the course of a week. I would definately advise any player to upgrade their IC after the first infra build. Being able to produce troops faster is an absolute necessity. You should never have more than 2k manpower laying around in the first two weeks of a game. You need fast unit production to achieve that. An extra IC and upgraded IC give you that.