Intel NUCs are IMHO exceptionally nice and fit your requirements, with some little caveats. Besides, it's a much more powerful machine and it will be easier to

Intel NUCs are IMHO exceptionally nice and fit your requirements, with some little caveats. Besides, it's a much more powerful machine and it will be easier to run till ARM becomes more popular. With some tweaks, in my experience it can use 3-4 W, so it might be able to replace a Pi in some scenarios. You might go slightly over budget with an i3 (unless you shop for a deal). You need to install a NVMe yourself, as well as RAM. The i3 can be run in a silent mode, but there are some third party cases around which let you go fanless. I don't understand why Intel is not selling a fanless NUC with an i3 / m3. There's a lot of potential. Same for AMD.