From the data usage you described, it seems that using a file based data store (Excel sheet, or even Xml/plain text) might be sufficient. A file based database, such as Access, or SQL Server Compact would alos do.
However, it is very likely, as most programmers/developers experienced, once you started collecting data, a snow ball starts rolling, and you would regret that you did not directly start with a good database system, be it for a small office or large office.
Many programmers working for a small office, especially when doing AutoCAD programming, tend to firstly look into Excel sheet, or maybe, MS Access, because it comes with MS Office and most people thought they know how to use it (especially for Excel sheet).
Data in Excel sheet/Access database can be accessed/queried with MS Jet Engine/Access Database Engine without running/installing Excel. However, AutoCAD 64-bit would causes some issues that would affect your decision of whether use them or not (e,g you need to install 64-bit MS Access Database Engine, which may be conflicting with MS Office installation).
There is other things that may affect your decision of whether you use SQL Server or other "simple" file-based data store. Such as data security, application security. With SQL Server, you can easily secure the production data, while using file-based data store, everyone who needs to use your app would have to have read/write permission. That means they are free to copy the file. As for the application security, since the app only be useful when connected to your custom database, which is secured in the SQL Server (that is, no one can easily get a copy of the database itself), so, even someone can take your app (exe or dll) away, they unlikely to get it work without connecting to the database. While with file based data store, someone could make a copy of both the app (EXE or DLL) and the data file and use it somewhere else.
So, in most cases, I'd go with SQL Server Express. In this case, I'd just do the development with SQL Server Express installed locally. Once the develoment is done, I'd duplicate the database to a production SQL Server Express instance installed in the office network, be either dethaching/attaching or backing up/restoring the database. Yes, there is quite steep learning curve of understanding how SQL Server is set up/managed.