'Serial' buyers - firms doing three or more deals - becoming more common.
Latest deal increases roster of partner firms to 27
Industry group sees trouble when brokers get out of paying back notes.
Fourth quarter flurry helped boost numbers over 2011 tally but just barely.
Small-firm seat on regulator's board is open; will be filled at annual meeting in August.
Advisers too busy adding clients and assets to pursue transactions.
Restructuring, if it happens, won't likely affect Merrill's advisers.
New hires to serve as regional directors; firm plans big advertising push.
