I run a web design company in Phuket Thailand, initally you costs need to be reflective of you area (geographical) at home (UK) id charge £400+ for a wordpress site buy here im lucky to get £250 - £300
wordpress sites are less costly as they take less time to develop from your end as all you really doing is taking a template and customising it as opposed to sitting in a room for hours typing out endless streams of HTML
I work on a 35% down to cover theme costs setup charges as i help with domain name purchases - hosting purchases i pretty much take care of everything for the client, this is a good and bad thing in some way as i have complete control over the project and its online presence - however i would not advise taking a contract for less than 35% down
Maintenance is better done as a monthly but to show good faith i usually say if anything goes wrong in the first moth ill take care of it, but i do provide a pdf on how to use the wordpress backend to limit the amount of times im called upon - i have 15 clients that i work with and i get a ton of referral work mainly due to the support and costs i operate on
Maintenance is general upkeep of the site (monthly) redesigns are one off payments and generally cover the entire of the site or at least and good proportion of them
I hope this helps
Gareth