5 man upgrade is a waste of fuel before your first tank in my opinion. I'd never make more than 3 infantry sections and usually when I've made 3 rather than two I wish I just made more snipers. Maybe against double Ost multiple infantry sections would be fine but they don't stand up to vetted OKW elites.
After the new patch I've found myself going for the 5-man upgrade immediately before my second IS. I will get 3 ISes in total, while saving myself a guaranteed 2x28=56 MP. 3x 5-man IS can stand up to any axis infantry unless you get suppressed.
Also How do you feel about sniper micro? I usually get one sniper for MGs and elite infantry, but going for more has a micro tax especially with heavy indirect fire and counter snipes. Your guide mentions aggression, but I find that easier in terms of preservation with ISes and grenades. Against any decent opponents, they will have AT before your first tank anyway so do you feel it's absolutely worth to rush every second of it?