What can I do to help improve the estimates with this query?
I would be more concerned with the 3 RID lookups on the same object8 farther to the left. can you change the index and INCLUDE those columns so the seek on Object8.Index4 returns those columns too?
But I doubt this is worth it. A more accurate estimate is unlikely to change the plan shape much, from what I can see.
The query already executes pretty swiftly, given the number of joins. The 867ms of NETWORK_IO suggests the bulk of the time is spent waiting for the large rows (LOB data, lots of columns) to pass across the network. You might get a better measure of the raw query performance by writing the results to variables (or a temp table).
If doing that really does drop the elapsed time for the query down to 1389 – 867 ~= 500ms, I'd ne asking myself how much quicker I really need it to go.