Some of the tools I've considered/used at my companies are Frontify, Invision Design System Manager, and ZeroHeight.

I think you will have good a learning experience going either route. The question is what type of learning you'd like to focus on at this stage of your career.

At a bigger company: You may be tasked to work on smaller projects as an intern or potentially paired up with a more experienced designer to work on bigger projects. For each project, you can probably expect to go through a structured and defined processes (e.g. multiple rounds of critiques, design handoff, design sprint, etc..). Because you're part of a big team, you're also likely to have the chance to meet, observe, and learn directly from other designers at the company. In addition, the company may also have the resources to provide you with other learning opportunities (e.g. events, workshops).

At a startup: You will likely be working on multiple (and potentially big) projects at a time. At times, you may or may not have the time or resources to polish up, get support on, or even validate your work. That being said, you'll probably learn a lot by doing and probably ship more projects compare to working for a bigger company.

Other things to consider: Since this is an internship opportunity and a step towards your full time design job when you graduate. You should consider whether having that big company name on your resume will help in your future job search. I'd also consider the connections that you'll potentially from working for either company, because some of them may benefit you greatly down the road in your career.

Best of luck!

taking this a step further, is there a way to import shared layer styles into the new file? (e.g. a set of typography)

You can also apply a thicker + different color border to a rounded corner rectangle in Sketch to simulate the nested effect. It may be a quicker approach but you won't be able to have a different corner radius between inner and outer shape.

One of the most significant change for me from an efficiency standpoint was switching from Photoshop to Sketch a few years back. Indirectly, it made me focus on the design itself more rather than making the software work the way I want it to.

I thought the Bee episode was very well done, especially with the mysteriousness and the final twist.

The hive technology as a concept is quite interesting and I can see the feasibility of the solution (as well as the vulnerabilities)

I've been browsing over stackoverflow UX from time to time to look for those. I haven't found a good source on the visual side yet.

You will be exposed to a wide range of tasks and most likely have a lot of freedom when it comes to making design decisions for the team (also depending on how involved is the rest of the team when it comes to design). It means that you will have the opportunities to learn things outside of one design discipline.

What I struggled with as the only designer in a startup is the lack of structure and support. Structure is something that you can define for yourself and the rest of the team you are working with. It does take time to get to a good balance of quality work vs the quantity of the design output.

The support aspect is probably the most challenging part and it's indeed frustrating to be the only designer at times. Not only you will be swarmed with many tasks being the only designer, you also don't have another design resource (designer) available to help you grow professionally. This is where you should seek outside mentorships or to go design events to make sure you are progressing.

In sum, I would personally recommend joining a startup as the only designer because I believe it's rewarding in different ways. If the startup is projected to grow fast, you'll actually be in a more position where you get to help build a team and that is an unique experience to acquire.