What special measures does one take into account to deliver lectures in classes including +100 students (compared to those of less-crowded classes)?
With 3 TAs you have a reasonable staff/student ratio. You need to use that staff to address the challenges a larger class size brings.
One of the main challenges is that the likely range of skills in the students is wider, meaning that if you want to afford an equal opportunity to everyone you need to work on making the process better for the strugglers who are willing but less prepared.
You also need to assure that marking of assignments and feedback are uniform over the class. In particular you need to produce detailed grading rubrics for everyone doing grading and you need to monitor the output of the TAs.
Keep in close contact with the TAs, with regular meetings in which they can bring you problems that need to be addressed.
Do some of the marking yourself, or, maybe just review the marks and (more important) comments that the TAs provide, perhaps by cycling through reviewing each TAs work periodically.
Lectures will be harder to manage if questions from students are to be considered. You might consider providing notes to students prior to lectures and a way for questions to be asked online so that lectures are more effective.
You might even want to think about the Flipped Classroom concept making face time an exercise lab with the TAs assisting the students.
In some fields, like CS, having students work in pairs can be effective as can group work with larger groups (say 3-5 students).
In my experience, a key thing about teaching larger classes is to keep in mind the scaling of workloads for different things. E.g. the time needed to prepare and give a lecture is more or less independent of the number of students, while the time needed to correct homework grows linearly.
This might seem somewhat obvious, but there are some aspects of giving a class that one tends to forget about, like all the organization that has to be done. If say on average one in twenty students sends you an email with organizatorial questions each week, that is barely noticeable in a small class, but if you are dealing with several hundred students that can result in multiple hours of work per week.
Part of this simply needs to be taken into account, but often there are several ways of doing things that scale differently. Stuff like preparing good lecture notes is constant in the number of students, but linear in the number of reduced questions. Similarly on the organizatorial side, a good FAQ and precisely worded instructions can work wonders. This will not stop some people from asking stupid questions, but at least it allows you to just point them a the information instead of having to repeat it in full.
Finally, keep in mind that TAs are not just additional working hours for tasks, but that they need to be managed as well. Most are highly capable individuals, but you will need to check in on them from time to time in order to make sure that things are on the right track. Also, while I am not a fan of hierarchies, keep in mind that discussion is the one thing where time spent can grow quadratically in the number of participants. So don't be afraid of telling your TAs how things should be done (e.g. by a precise grading rubric). You should still listen to their feedback of course, but sometimes a quick suboptimal decision is better than endless discussion about minor details.
In particular the latter might not be too much of a problem with your example of around 100 students and 3 TAs, but I have seen classes of "Math for everybody" with 1000+ students and 15+ TAs, where organizing in itself was more or less a full-time job for one post-doc and each exam was a logistical masterpiece, taking weeks of preparation.
The other answers cover the most important stuff, I think, but haven't touched (much) on the classroom component of the course (I'm assuming this course is being delivered in-person ...) @Buffy mentions lecture management, but here's some more detail.
- the lecture room will be a lot bigger, you'll need to carefully consider visibility/legibility of materials. Working on a blackboard (if you're in a discipline that does this) probably won't be feasible any more, you'll most likely need to work with a document camera or write on a tablet that's connected to the A/V system or write on a touchscreen if one is provided. Figure out your presentation technology and visit the classroom in advance to work out the details. You should also figure out where the light switches are, how they work, and what the best setting(s) are.
- Student engagement gets harder. Clicker/polling questions definitely come into their own for large classes. Find out what system(s) your institution use(s) — are students already buying clickers for another course? Systems like PollEverywhere are phone/tablet/laptop-accessible, but also require payment [either from students or from the institution]. "Think-pair-share" approaches can work, with students working with whoever happens to be sitting near them and reporting results via clicker. There are no/low-tech approaches as well — these approaches were originally developed by Eric Mazur using coloured cards students could hold up — but the technology-assisted versions work well, can allow you to assign low-stakes credit for answering questions, etc..
If the course is online, there's a whole other set of presentation-scaling issues to consider ...
- Will whatever online system you're using to present (Echo360, Teams, Zoom, WebEx, ...?) handle your class size gracefully? (There was a minor disaster at my university on the first day of fall 2021 [I think] when instructors realized that the university's Teams license didn't cover >1000 students in a meeting.)
- do you have your system locked down to avoid outsiders crashing your class, or disruptive students within your class? (This can be an issue for smaller classes but gets much worse for larger ones.)
- Do you have a TA moderating the chat/question-and-answer channel?
All of the issues raised by other answers about "if you have one problem student in a class of 20 you will have 5 problem students in a class of 100 and 50 problem students in a class of 1000" apply here, but now you have to manage the problem students remotely ...
Your lecture should be thoroughly prepared, no matter what size the audience is.
Your writing should be visible to all. A digital overhead projector is better than a blackboard. Plus, it can be recorded along with your audio.
Your voice should be clearly audible to all.
Dealing with disruptive students is the hardest part. Even just sustained whispering among a small bunch of students will significantly degrade the experience for the rest of the room, but addressing the offenders can easily end up with them filing a spurious complaint against you.