The simple answer is NOTHING
There are a few extra things you might consider in the very immediate short term. If you don’t have the very latest version3.9.141 (you can find this on the about item under the help tab) it is probably a good idea to at least download the latest version, which according to the google blog will only be available till the 15th. March. I have downloaded this version and it looks a lot like version 3.9.140 (which I’ve had on my machines for a while). This version shows upload to google photos on the big green button at the bottom of the main picasa screen, and seems to work, but bizarrely when I try view on-line it loads internet explore (whereas chrome as my default browser), but it lands on a page that introduced the google photo apps for android and IOS, but looking around there is a red goto google photos button that first ask me to log in with my google account, then recycles the screen and this time ask me to also put in my passwords and then finally I can see my photo. Not exactly simple, probably best avoided in future (see below).
I already know an elegant way to share photos privately with just specific people via an email link, that is just the basic dropbox. Something I’m sure you already have. If you want to automate this a little, get the drop box app for your PC and this sets up a drop box directory under your user account. One of the default directories set up is called photos. Now using the export button all you need to do is the change the directory to that dropbox location. Any new export folder then becomes a separate album and the whole album or selected photos are easily shared, using drop boxes share with tools. This includes setting up collaborator two way sharing. With a two-way share you can also the add folder to picasa and set up the scan always so the picasa view is always up to date.
One final thing you might consider is making sure google doesn’t keep watching you and/or interfere (albeit unlikely). To do this, find the Options Tab under the tools item on the main menu, and untick the send anonymous usage stats to google item under the general options tab.
There are a few things to do to ensure you can migrant your collection’s organization to other packages but that can wait for another post.