Unfortunately, due to the reactor array using 1500 CPU and the silos using 500 CPU each, a medium reaction cannot be done on a small tower. It requires at least a medium tower and since they use twice as much fuel as a small tower, reacting will cost you twice as much per week than simply selling your raw materials. Take this into account when assessing your profit margins.

THE BIG MONEY
The final step in the moon-mining chain is the complex reaction. As you can see from the Reaction Table, intermediate materials can be reacted together to form advanced materials like Crystalline Carbonide and Ferrogel. Unlike simple reactions, these cannot take place in a medium reactor array but must take place in a full-sized 'Reactor Array', which uses twice as much CPU as its medium counterpart. Due to this, medium towers are not suitable to run a complex reaction. Instead, complex reactions must be run on large control towers only.

Also, unlike simple reactions, they may take up to four different intermediate reactions to produce a single product, as is the case with Ferrogel, and they do not produce 200 units per hour but rather a large amount which varies from reaction to reaction. If in doubt, check the Reaction Table or look up the reaction blueprint info in-game.

These advanced materials are then used to build Tech II components which are used to build Tech II modules, ammo and ships. Since producing advanced materials is the ultimate purpose of moon mining, they sell very well, more than justifying the double fuel bill over a medium tower and the 500-700 million ISK price tag on a large control tower and modules. Selling intermediate materials is often very difficult, but if you can react them into an advanced material, sales will be swift and more than worthwhile.

FUEL PROXIMITY
Starbases use ice products from refined ice as fuel, as well as NPC-sold industrial trade goods. It is a good idea to have your fuel supply nearby the POS to minimise hauling when it's time to refuel and haul the product back for sale. One successful fuelling strategy, and the one I use myself, is to keep a stockpile of at least one week's fuel in the corporate hangar array at the POS, then top the fuel up daily from that. The stockpile has one week's supply added each week, at the same time that I haul the product back to the nearest station. This means I only need to actually haul to and from my POS once per week.