Science & Industry

First you'll need to make sure production efficiency skill is trained to level V. Anything less and you'll not make a profit on most items.

Next you'll need a BPO with a high ME level, which you can research on your own, but with ammo you might be better off just buying a pre-researched one for a premium price.

And finally with high volume low isk items like ammo you wont make much if anything selling in trade hubs. All the profit from ammo comes from seeding it in stations where there may be a demand, and then selling it normally at a higher price then the trade hubs (but lower then anyone else in the station). Ammo is one of those things people buy all the time and all over the place, so you can easily set a high price on it and still sell it almost everywhere.

And with ammo don't sell it to buy orders, instead setup your own sell orders. Selling to a buy order just means you are selling it to someone who will re-list it and sell it at a higher price, so skip the middle man and sell it yourself. Sure you wont get instant isk, but you'll get more isk over time.

Yeah, all depends on the type of item. Some don't make any money, some do. Some do but take months to sell.

Industry is really about knowing the market more than knowing how to build stuff. Once you can build an item, you probably won't lose the ability to do that. The market can change on a whim.

You might want to play around with the program in my sig. Not really for beginners but it might help. The manufacturing tab lets you compare different types of items against one another.