I would use subfolders to run your niche sites, so you would have http://fromwales.com/leeks – this way you can run as many niche sites as you want and link build to each folder if required.

Google views sub domains as separate websites therefore any website authority your domain has will not be passed to the sub domains. If you were to use sub folders authority is passed to the subfolders, therefore making it easier to rank for desired keyterms meaning you will need to build fewer links.

Although sub domains are still being used and in some cases the correct method to use, Google understood that spammers were using sub domains to rank for multiple listings in Google.