Building a singlespeed road bike for general use about town, and need a bit of advice. Firstly can I use a normal chain or does it need to be something special and secondly what is the best chain tensioner to use as frame has vertical dropouts.

you can use a normal chain.

The Surly Singleator tensioner is good. I tried an on-one first but just couldn’t get it working proper. Surely working a treat.

I also have an on one that i am struggling to setup, it seems to not be able to hold the tension properly and leans?

You can use a normal chain, but because you dont have all the gears and such you can go for a thicker chain, which wont snap as easily when you putting the power down.