You'll find you're whizzing up to level 50 in no time. I was level 9 after only two games last night thanks to a combination of the xp multiplier and my full deck of burn cards (first game after prestiging is the perfect time to use those otherwise useless "fast xp" cards, "kill grunts/spectres" cards, etc. Save the titans and amped weapons for a game or two, and use them when challenges become unlocked).
I tend to switch weapon (to another rifle or smg) after I've got 50 kills or so, just because you get access to lots of new challenges (so extra xp as well as amped weapon burn cards), and my current 1.5 multiplier means I'll be level fifty well before I've done the trickier challenges.
On tenth generation you get a 3.5 multiplier. You could probably get to level ten or twelve after only one game!
The auto-pistol is actually a fairly decent weapon. It has a pretty big clip, and fires as fast as a SMG, so you'll manage that requirement pretty easily - so long as you remember to switch from your primary weapon immediately when you spawn. I kept forgetting.
I didn't much like the sniper rifle, especially as it sometimes requires 3 hits (though it's one hit kill if you get a headshot, natch) but it is semi-automatic so you can fire it relatively quickly. Good if you can find a decent elevated position near the edge of the map. From high up on the edge you can get people who are on the ground as well as those sniping from high up in the middle.
I found the Training Grounds level good for that, as there's a ledge you can camp on right on the edge of the map near Objective C, in Hardpoint mode. You can see half the map from there, you can pick people off the big roof in the middle of the map, and you can snipe those trying to capture the nearby hardpoint (people tend to hide in the corner of the room, there, and you can usually see them easily from that ledge). There's probably similar positions in several maps, though.
I get the impression the new game modes will be free, whereas new maps will only be available if you pay. I believe there's going to be 3 map packs at $10 each - or you can get a season pass for $25.
Will probably buy the first map pack "Expedition" when it comes out in May - though it's disappointing that there's only three new maps in it.
I believe we might be able to customise the titan paintwork and logos in an upcoming DLC - but I don't know whether it'd be in the free or paid DLC. It's a little gimmicky thing that adds nothing to the game really, but I love that sort of crap
Have seen my K/D creep up from 0.8 to 0.9 and now 1.0 this week. Was worried it might dip a bit over the weekend, because I needed to do the Charge Rifle challenge - so spent all my time in stupid positions I wouldn't normally hang around in, firing a bloody big beam of light all over the map just in case there were one or two people who hadn't spotted me up there - but it stayed fast at 1.0