It depends, most of them will work with few fixes on the .xml views, others will work with a few fixes on the .py, because model relationships and fields that now doesn't exist (specially if they have a res.partner.address relationship, I didn't see many big changes in the database structure). Other complex modules could need a lot of work. If someone could provide a link with relationships and fields changes it would be great.

One way is to run open in debug mode, then try to install the module, then check the errors, fix it, install, check errors, fix it, and finally test it.

copy/paste module in addons on v7

then login as administrator and edit default administrator's account user privileges, and turn on "Technical features" (disabled by default)

then you have to reload page so new menuitems show (or open some other page, logoff/log on) Anyway now should be visible menu option Modules -> Refresh module list

hint: to install module from tree view-> goto Installed modules, and remove filter 'installed' (default filter for view), now you can see full list of availble modules nad filter/search for desired one, also from this view you have the option to actualy install them :)

... that shold be it.. after this point it is the same as in v6

... careful with instaling v6 modules, some fileds are different in v6-v7 so not all modules will succesfuly install..