In working toward a full handstand, I'm scaling by starting on the wall and holding my form for as long as possible. The question I have is around handstand technique--particularly elbow locking. There's a point at which I feel my elbows lock into place when they're completely straight, which isn't painful and makes holding my form for longer periods of time significantly easier. However, I'm not sure if this increases the potential for injury or would impact a smooth transition to handstand pushups. Curious to hear your thoughts as to whether or not locking in this way is good idea.
TL;DR, locking your elbows is fine.
"Locking" one's joints is simply bringing them to the maximum range of motion. It is the strongest position that you can be in, because you are using your body's full strength and durability (you are also more safely strengthening the connective tissue). The one exception is where you're applying sudden force to the limb where you need to absorb some of that force. The classic example there is bending your knees when landing from a jump. For a static hold like a handstand, you want to lock your elbows.
Under general caveats, as mentioned below, it can be a bad idea to lock your knees on something like a weighted leg press. This is in part because knees hyperextend relatively easily, and the amount of weight can cause damage if it bends them backwards. In general, maintaining hyper-extension is a bad idea, but it tends to feel so uncomfortable that most people won't stay in that position for long (leg presses can be dangerous in that respect because you're used to bearing weight on your legs due to standing, so it's easier to "hold" there and not realize the discomfort). Also, while the mechanism is sometimes debated, standing with locked knees can lead to fainting. My best understanding is that it actually has less to do with locked knees than it does standing too still, causing blood to pool, or with general over-exertion such as hot weather and heavy uniforms. With locked knees, you're not moving your muscles to encourage blood flow, and you may be less likely to realize that you are getting faint because your knees don't start to buckle first, which means it hits you all at once.
Another caveat, while I'm at it, although I don't think it applies to you, not everyone can lock their joints in a straight position. Some people aren't flexible enough, or are too flexible, and have to work in a less than fully-extended stance.