First of all, you wont get a bot with 4 industrial slots. You will get a combat bot which is able to use only two mining modules.
Transport missions are good for fast gaining of reputation which helps in manufacturing, but if you dont have access to the free movement on beta island (neutral bots being destroyed without any warning) this have no future. So try mining, its profitable too. Just buy an Argano and do some mining missions to know where is what to mine and gain extra credits on it.
About EP: If you're going to mine you're gonna need a Termis, this mech requires lots of skills for comfortable and efficient operating. You need to train skills to increase your capacitor, recharge and skills which reducing power cost of your medium mining modules. And dont forget to train skills which unlock this Termis for use.
UPD: You can craft whatever you want even right now, like light bots or ammo, such thing allways on demand. You just need an example of what you're going to craft and a decoder. But you will lose many materials, so train skills to increase factory minerals efficiency and gain reputation doing mining or transport missions.
Good luck.