Midi And Audiointerfaces, help for a newbie? Options

[black fly]

hi together.
i just purchased my first mac for making music. system is os 10.2.1
my equipment is: 2 harware synths, a midi-keyboard and a harddiskrecording-system (yamaha aw 4416). i want to combine this and the mac. maybe some days later i want to buy another hardware synth, but not yet. sequenzersoftware shall be logic 4.81 and my wish is also to use a software sampler like ni kontakt or others. not to forget about plugin synths.
my questions are:
1. which midi-interfaces (8 i/o) can be recommended? can i take used ones, and when, which?
2. audio-interfaces: is it better to work with an interface or a card?
as i´ve been working only with hardware(no computer) during the last 2 years my knowledge about this is outstanding small and i would feel very happy about some advice.
greetings,
alex