"More wires" isn't going to solve anything. Your upload from your ISP is going to limit the speed (and quality) of what you can possibly hope to stream over the internet. Also, depending on how you build your Freenas box (assuming you're going to stick with Freenas for your new build) will also, in part, define where and how your server bottlenecks. Internal streaming is going to, in large part, be defined by what sorts of router you are using, whether you will be running cable or attempting to stream over wifi, using 802.11AC or N, and externally, it's a question of ISP bandwidth.
Freenas on an old laptop is fine as a "proof of concept" or for simple streaming internally to your own client devices on a LAN, but to use Freenas properly, you need/should be using a much more robust system than an old laptop. Minimum, you'll need a Gigabit ethernet port (most old laptops had only 100), and with Freenas 9.3 and above, you will need a crap-ton of memory to properly use the ZFS file system which means if you care about your data, a lot of costly ECC memory, and a decent mid-to-higher end Intel or AMD processor (although most Freenas afficianados will tell you Xenon or i7's), and a dedicated Asrock motherboard built to work as a server, and not some crapware cheap gaming board that may fail in a year or less. Solid HD's, generally WD Reds at a minimum, and perhaps some SSD's for cache.
Once you get your server built. these are the three things that will limit how many clients/people to whom you can stream: Processor Speed, Upload Speed and Hard drive throughput. If you are streaming direct both LAN and WAN, (i.e., without using something like Plex), that uses more bandwidth (of which you don't have a lot). If you use something like Plex, that transcodes whatever you are streaming, and would likely improve your situation. The purpose of transcoding is to drop the stream size down to a more reasonable level. In most cases hard drive throughput won't matter unless you are streaming multiple streams off a single harddrive or if the drive is connected externally via USB 2 etc. Processor speeds only matter if you transcode multiple streams at once. If you directly stream a file (i.e. over local network) you likely won't see any processor usage.
For streaming to others, upload speed is king. If you had a high upload speed, you really wouldn't need to be concerned about transcoding, but if you have 10mbps up speed and three to five people watching, you would need to transcode those streams down to 2-3 mbps for them to stream without buffering. Five transcodes at once would require a higher end processor, so keep that in mind when you do your new media server build (or when you buy one).
The best scenario, if you have a lot of friends who want to watch from your library, is to get Plex Pass to enable syncing. It transcodes and then stores on each client's local hard drive so it takes some of the burden off of your upload speed limitations (and your processor) since it doesn't need to be done in real time. I do not use Plex Pass so I am not familiar though with how it actually treats multiple users (i.e., there may be limitations on the number of simultaneous users you can serve to).
Anyway, welcome down the rabbit hole....your adventure has just begun with media streaming.....good luck.
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