So I started playing xcom on normal for a few days then learnt about the Iron Man mode and decided to get on that straight away, decided to go classic. For about the last 5 nights I have played a new Iron Man game for a couple of hours and then I either lose too many soldiers or lose too many nations, as frustrating as it can be when you miss a 85% point blank shot and the next turn you lose your best soldier, I wouldn't play it any other way.

What should I be investing my money in? What is the best stuff to research? And all sorts of tips that helped you guys.

A few tactics I've learned. They're applicable to everything, really, but Iron Man makes everything that much more valuable:

1. Never move further than the first unit you move. If your first unit causes aliens to scatter (activate), you can still use the rest of your units. If your last unit causes aliens to scatter, you're at their mercy once it's their turn. Also, since you've activated them, they will fire at you.
2. Don't forget that you have grenades. They're 100% accurate, and will always do the damage they're supposed to do. Also, they'll take out cover.
3. If a unit isn't in full cover, really, really consider using Hunker Down instead of Overwatch. This was the first thing I changed in my playstyle when I went from Normal to Classic.

As for strategies:

1. Satellites are still the number one thing to go for. Always be building satellites.
2. Don't skip lasers. It's do-able on normal, but your combat effectiveness will get blunted pretty quickly on Classic if you go straight from conventional guns to plasma weapons.
3. Consider going for the Arc Thrower and Alien Containment off the bat. You're going to have to capture an alien to progress, and it's a lot easier to stun a Sectoid than a Muton.