Hmmm, well the expenses of the hobby has led to me not really painting or playing for a while, but I read the books (Black Library has some good [censored] in there) and I stay up to date in new models and stuff.
Though I do admit I am more into Warhammer Fantasy, I jsut like it better, been thinking about rebooting it mith a new army etc. Though the Orcs and Goblins are fun, if I choose wisely I can still use my giant though.
I have played some 40k, but it's like 2 editions ago, I have some orks. Though if I start again I will probably roll with either Space Wolves or Chaos Space Marines, because I like chaos in both settings (in fantasy the chaos warriors are vikings too <3) And the spacewolves are like werewolf vikings, which is just bad-ass as hell. I have also been thinking about Salamanders or Lamenters, the Lamenters are pretty cool. Or I could just go anit ork and get Crimson fists, crimson fists are pretty awesome.
As far as suggestions, get the army that you like, I know some people who are way into the rules and what works competatively. I'm more the kind of guy that uses the models that look cool and the army with the coolest models and coolest fluff, because the lore is pretty awesome. If you have time I would recommend getting into the lore. Some armies are cheaper than others as they have models with higher point costs, so you won't have to drop as much cash on them.
It seems like you have found your army though, Deathwatch, which I've never played against truth be told, I mainly played agains Space Marines, Chaos and Imperial Guard. Anyways they have some cool lore, though a lot of the lore depends on what legion they originate from as the deathwatch has people from a lot of different legions. Some people consider it the army you choose when you can't make up your mind about what chapter to use, but who cares what they think.
If you're feeling the hype there are as I said tons of books (Horus Heresy, short stories, different trilogies and stuff, I am currently reading the Word Bearer trilogy) there are also tons of video games though the most popular ones probably is Dawn of War, which is a great RTS series, you can even select the color of your army etc, it's fun. Dawn of War 2 is way different from the first one though with no base building, but it's a fun game and the last stand game mode is pretty entertaining. And if you're into shooters Space Marine is worth a buy. I haven't tried space hulk yet, and storm of vengeance looks like crap, but there is Eternal Crusade coming out this year and it looks pretty dope. But as I said this is if you're feeling the hype.
If you are looking for tactics tips 1d4chan.org has a wiki that has tactic tips for most armies, could be worth getting into, they also have some fun comments on the lore etc. though if you want to get into that I reccoment the Lexicanum wiki. Anyways the main point is that you're having fun.
Oh, is the Deathwatch army yours or? Do you have your own army yet? Because re-picking your army is never fun, waste of money. Trust me, I got some necrons and some dark eldar and some normal eldar around somewhere. Oh and buying a battleforce is a great way to start off your army and it's mostly useful units in the box.
Oh and if you feel like becoming extra poor, you should check out the forgeworld models they look awesome and they will only cost you your 2 firstborn children.
Oh and if you see models that you like, but that aren't in your army list there is always the chance that you may use them as allies.