I have a new Roku device, Roku Ultra LT Streaming Media Player 2019 - Model # 4662X (Website said 4662RW), and a Roku Model: 4200x - Roku 3. I added a micro SD card to shorten the startup time on the new one, but the old one doesn't take a card. It does have a USB port. Can it be used to increase memory? Barring that, I'm wondering if I reduce the number of channels on that Roku device, will it speed up the start-up time? Any other suggestions?
Adding an SD card doesn't make the Roku boot any faster, not operate any quicker either. All it does is allow storing more channels before needing to off-load to install a new one. In that respect, it will speed up starting a channel, since it doesn't need to download the code again. But if the channel is already in local storage the SD card doesn't make the Roku any faster.
You also asked about the USB port. No, the only thing you can use the USB port for is as a media source for playback via Roku Media Player. The Roku has no ability to store something on an attached USB device, it's strictly for media playback only.
Dan Roku Stick (3600), Ultra (4640), Ultra (4670), Premiere (3920), Insignia 720p Roku TV, Sharp 4K Roku TV, Nvidia Shield, Windows 10 Pro x64 running Serviio and Plex on a wired Gigabit network.