what are my options for this route ........ are there plenty of trains from dm to hl?? ....... is it still a long wait for taxis?? ........ or maybe taxi to to nearby mrt or bts station??

The train is one option, but takes about 1 hour.

For train check here: http://www.railway.co.th/checktime/checktime.asp?lenguage=Eng

Another is the airport bus to chatuchak park and take the subway from there.

Than there is the taxi.

It always helps to explain why you need to get to a location, pertinent travel info (pax nos, baggage, is money an issue etc), time & day of arrival to illicit useful info.

It may be that you don't need to go to HL if you are catching a train, http://www.thaivisa.com/forum/topic/636035-don-mueang-to-train-station/

Give some more info and you'll get the info you need.

The above info is take the A1 Shuttle (check the other threads for info ) to Mo Chit BTS station/MRT Chatuchak station and take the MRT direct to HL (about 25mins)

http://www.bts.co.th/customer/en/02-route-current.aspx

To answer your taxi query, yes taxis from arrivals are still a problem. Always take one from departure levels except after 10pmish when there won't be many dropping pax off.

At that time, it might be quicker to head to the main road, Vihavadi, by the pedestrian link for Amari Hotel/DM Railway station. (Though it is not easy walking down the stairs to ground level with a large bag or for those with walking issues). A much longer walk at ground level from arrivals can be done to the main road.

illicit useful info.

Illegal information? Maybe you meant "elicit"?

Seriously, agree more details are helpful. Some trains departing Hua Lumphong pass Don Mueang; while most/all pass Bang Sue, where one could catch either saving some time, and even allowing one to catch a what looks like a tight connection train, remembering that most SRT trains actually depart ~1 hour late, and are lucky to get to Bang Sue ~ 2 hours after scheduled departure from Hua Lumphong!