Hi Marike,
unfortunately I personally would answer both questions with "yes".
To sum it up: a change of domain names is not the best thing from SEO perspectives. But of course there are many situations in which this can`t be avoided and where SEO has to stand back.
The change/merge of a domain has always a certain impact on the rankings which have been established by the old one. I highly recommend you to use a 301 redirect or several if neccessary - they pass the PageRank for example.
Furthermore you should use the change of address tool in the GWMT - it`s used to tell Google that the address of your site has changed.
If youve done the work youll have to be patient. It might take some time until you get back all of your old rankings. In general this doesnt take soo much time but Ive experienced that there is a big chance that you wont get all your old rankings back and that those positions arent written in stone... well this aspect is also valid for well established domains.
Best regards, Marc
