OK. The ships can be found in any sector that is termed a "homeworld" (i.e. zoltan homeworld). There'll be a little quest thing you'll have to do. The Engi ship you just get if you get to sector 4.
With the first ship you've got, you want to have at least 2 shield by the end of the second sector. That means saving up 100 scrap (with the extra energy you'll need.)
Leave the medbay unpowered until you need it. If you can fight boarders in a powered medbay then do it, cos you cannot lose.
When fighting enemy ships it's all about containing them. Destroy their weapons as soon as you can. You want to hit shields if you can't get through otherwise but you have a burst laser, which fires 3 shots and nothing has 2 shield until sector 3 (on normal, don't know about easy.)
Time your shots. Don't fire as soon as it's available, use a laser to knock shields down and then hit em with a beam. Stuff like that.