Try posting screenshots to the users forum to get some feedback.

There's several approaches you could take for the estimates:

1. Add a row that displays "Estimates: None" or "Estimates: Yes" with the "Yes" being a hyperlink to Customer|Estimates.

2. As above, but only display an Estimates: ... line if there are estimates, to save on screen real-estate.

3. Display a small estimate icon on an existing row (no idea what one looks like however).

The following is a more efficient way of determining if a customer has estimates.

IIRC, the ResultSet approach will pull in up to 80 records if they're available.

import static org.openvpms.component.system.common.query.Constraints.eq;
import static org.openvpms.component.system.common.query.Constraints.gt;
import static org.openvpms.component.system.common.query.Constraints.isNull;
import static org.openvpms.component.system.common.query.Constraints.join;
import static org.openvpms.component.system.common.query.Constraints.ne;
import static org.openvpms.component.system.common.query.Constraints.or;
// snip

boolean hasEstimates(Party customer) {
        ArchetypeQuery query = new ArchetypeQuery(EstimateArchetypes.ESTIMATE);
        query.add(join("customer").add(eq("entity", customer.getObjectReference())));
        query.add(ne("status", EstimateActStatus.CANCELLED));
        query.add(ne("status", EstimateActStatus.INVOICED));
        query.add(or(isNull("endTime"), gt("endTime", new Date())));
        query.setCountResults(true);
        IPage<IMObject> page = ServiceHelper.getArchetypeService().get(query);
        return page.getTotalResults() != 0;
}