For one site of mine, I'm thinking of switching to WP platform from static pages. What can be the risks (rankings etc), if any, involved with this move? I'll make sure content, heading tags, meta, title etc on WP pages will be same as of static pages.
if you do a major layout change, then you usually expect to see temporary drop in ranking at the beginning. with static site to Wp is a big move with totally different layout and navigation structure. depending on how competitive your niche is and where you rank, it might take you some time to recover the ranking drop if there's any. i would suggest you to do some link building immediately after the change. one good idea would be to use your feed on the forum since you have lot of posts. this way googlebot will follow the link and crawl your site often. usually the ranking drop that we see after this kind of change is only temporary and with some link building, you can get back in game
the biggest risk is to back links and lose of traffic from theose link as well as the PR juice.. You can have a home.php or leave your static page where it is and then structure your wp install pages and posts so that it reflects the same structure as your static site. there is an option in wp where you can install wp in a directory other than the root and reflect it so it appears wp is installed in the root. do not forget to change permalinks so that rather than %postname% it is %postname%.html
It may put your site back in the google sandbox, but if you have strong backlinks and high pr it may only take a month to recover. It really depends on your niche, just create new unique original content and keep building backlinks to speed up the process.
i have switched a lot of my static sites over to WP - it has been a good move in my opinion. Most of them rebounded extremly fast and ranked better and easier in the serps