A quick update.
Easy enough to upload DNA results to My Heritage and FamilyTreeDNA.
I had strong confirmations to someone I had already made contact with on ancestry.
I also had a strong connection to the brother of an ancestor born about 1790s and it would have been interesting to communicate with this person. However they have not replied!
I find a large number of the DNA connections never reply to my e-mails. What am I doing wrong?
To answer your final question, probably nothing. Everyone who has messaged people on Ancestry will tell you the same - many, many inquiries go unanswered.
There are many reasons why - the person may not have been doing family history research for a while, they may have lost interest altogether, they may not be interested in connecting with other people, they may only have done the test for the ethnicity estimates, someone else may have bought it for them, and of course they may just be too selfish or rude to bother to send any reply.
The one thing I have found is that I have a higher success rate when, at least in my first message to someone, I keep the level of detail relatively small, i.e. something along the lines of "I think we may be related through x, who is my gggg grandfather, and seems to be the grandfather of y who appears in your tree" or something like that.