I am not saying it is amazing, but you said worst skill. Several people have posted skills which are arguably more useless as well as reasons why this one isn't actually terrible. If I'm comparing worst skills I would probably go with Razor Edge, closely followed by Vitality Serum and Sector Ranger. There is no reason I would take any of those while I did have the self heal for a while until I got Lokin as a companion. I'm tempted to take it again for operations as adrenaline probe is used on cooldown and it would take some stress off the healers.

Energy is a mechanic that a lot of people just don't grasp initially. You do more damage over the course of a fight if you keep your energy abouve 60% (4 of those little arrows on your energy bar) than if you blow it all at once and then wait for it to come back slowly. This isn't like WoW rogue energy or jedi force which has a constant gain rate. Just use specials when energy permits and interweave the energy free attack (rifle shots) to keep using GCDs. And if you had 60% energy when the tank dies it would help with burst.

Dead snipers also do no damage. I don't see how you can prioritize 4% health over 6% self healing on a 1 min cooldown. Granted if you are biochem it's fairly useless, but not everybody is yet

I tend to agree. Personally I liked leveling as Engi because it made dealing with the packs of mobs pretty trivial as they would all die between plasma probe and a grenade. I've also found it made energy conservation pretty easy with EMP blast resetting adrenaline probe on a 1 min cooldown. Since threat = damage I am guessing it is fairly good DPS also because I am always the first one to die after the tank. (Where are you combat logs)

Pretty much every other planet has a commendation vendor that sells weapons. Once you find a model and texture you like it is just a matter of buying the hilt (or making one) to upgrade the damage of your saber to be in line with your current level.

Check the GTN. Like the poster above me said it is not a schematic it is a one use consumable. The mission you get from that is usually much better than your average mission. Luckily you can buy the consumable mission items off of the GTN because slicers find them running their missions. Just be careful what you pay for them. It usually provides a lot of benefit, but people tend to be dumb and significantly overprice their GTN auctions.

Don't forget about his transformation ability. Against easier groups of mobs it's quicker to transform him and let him beat them down before swapping him back to healer mode. Personally I tend to run with either Lokin or Temple. She's great vs the easy stuff if you put her into AoE mode. Between her AoE and mine we blow up small packs extremely effectively. Groups with multiple silvers or elites I break out Lokin and try to cover tank them with him healing me. Kaliyo doesn't get used much since she's a mediocre tank (even though I just got her a bunch of lvl 40 pvp gear) and she often doesn't like my dialogue choices.

Marauders get Vette not Mako. Snipers do tend to have a lot of burst. Welcome to playing a DPS class. You will cause a lot of threat and get yourself killed if you don't pay attention. Leading off with all of your heavy damage abilities will usually cause the mob to chase after you. Solo this is advisable since you want it to die as fast as possible. When grouping, especially with an actual tank, it is probably best to start off slower to give the tank a chance to generate a threat lead. If you do plan on using Kaliyo to tank make sure she is in tank stance and not DPS stance (tank stance looks like a flexed arm). It is probably advisable to do this as your friend isn't really a tank class so he'll get beat up fairly quickly as well. And since you are using her to tank just remember our self heal ability (recuperate) also heals the companion so you can keep her topped off before each fight.

Interrupts are big when taking on elites past around 35. Depending on what you are tackling some of them just have too much HP. My biggest problems come from stupid jedi knight elites. They get in my face and prevent me from using cover to ignore some of their attacks and specials. A lot of them have the audacity to even be immune to cover pulse. Whenever I can't utilize the benefits of being in hard cover due to the melee nature of an elite mob I switch tactics and tend to kite them around and use Lokin. Engineering spec has a permanent 30% snare and that combined with explosive probe and other instant attacks makes it annoying yet doable. I would almost have to say that hard cover is a necessity when taking on elites. The fact that they can't hit you with normal attacks (and some specials) when you are down means you take a lot less damage. You can switch up your tactics and blow a lot of your energy in one big burst and then drop down and let it regen while you take less. Using shield probe while you're out of cover will let you DPS while taking no damage. Use interrupts to stop the specials that can hit you while you're in cover or entrench to ignore the knockback rocket type attacks. If nothing else when the elite is pissed off at you that means it is spending its time pointlessly shooting at you in cover while your companion continues to chip away at its health. Sniper certainly doesn't benefit from the "stand there and shoot them in the face" strategy like you do with BHs and some of the jedi classes.

One of your later companions has an investigation bonus.

There is overlap. I know for certain I'm seeing both tier 4 and tier 5 scavenging on Hoth.

The 'crew' in crew skills is describing crew members as a whole not each individual crew member. So while you get multiple companions your entire "crew" can do three skills total. Only one of which is an actual crafting skill.

Sorry coffee hasn't kicked in... I didn't realize there was a level 25 one since I just used the free one until 40.

Orange reskin of the level 40 bike. The higher level mods are learned from a schematic so either they are a drop or super rare from top tier slicing. They require a BoP item from the bosses in hard mode flashpoints so there is a good chance they drop in those.

That isn't even close. Can't post screenshots of my own from work, but here are examples from the internets. Level 40:http://www.youtube.com/watch?v=c4zRO6uKW2w Level 50:http://www.youtube.com/watch?v=BK97xII2vQk