Bike help

all right i posted this in ns bikers but its dead so........

i think im going singlespeed. i have a question though, i have vertical dropouts and i really dislike having a tensionner. can i just buy a sprocket and spacers and be fine? i havent figured out the teeth ratio/amount yet, but if i get the perfect combo, wouldnt it work? cause the chain would be tight enough and not ever move?

then i saw half links... can anyone explain these to me?

if worst comes to worst, maybe ill invest in a tensionner, but id love to hit the perfect teeth ratio and make it work....

thanks