If your enemy has decent shooting and goes first, you will propably loose your stormraven and most of the hellblasters (4++ can only do so much for them).
If you can make the scenery work for you, the hellblasters can be great, but try to hide them out of LOS.
Also, I know the techmarine will feel lonely, but i would still let the knights teleport in. Belive me, there is nothing more sad than letting DW Knights walk across the battlefield.
While tacticals may not be the optimal troop choice, I dont think they are that bad. At least your opponent has to kill 4 marines before he kills the lascannon.
Still seems like a fun high risk, high reward list.