I still have Java disabled on my computer. I haven't heard anything about that it's safe yet. Is there any current information on whether Java is safe to use yet?
Relying on fixing and securing all the individual PCs, Macs, tablets, etc. is a futile quest. It's better to focus on maintaining security in the network devices. If no one can get to your HTPC, then running Java on it, or any other software, is "safe"
Check the manual for your firewall/router, and see if it can support VLANs. It's a corporate level networking IT feature finding it's way into the more recent home consumer routers (past 2-3 years). If it doesn't, I would recommend buying one, and setting up multiple VLANs configured to your needs..
VLANs are "virtual LANs". All your ethernet cabling remains the same, but now you can set up the router with several sub-nets and assign one or more devices to run on each (unique) sub-net. Then you define security rules for what traffic (if any) can flow between VLANs (sub-nets).
I have one VLAN for all the HTPC related equipment in the house. Another VLAN connects my kids computers to the internet only, but the "Kid-net" can't exchange traffic with the HTPCs and my computer. So if their machines gets hacked, they can't attack any other machines in the house.
The "Vid-net" isn't route-able to, or from, the internet; so for all intents and purposes it's on it's own separate protected network. When I travel, I have temporary rules to allow access from my iPad, and only my iPad, to the Plex server.
You can set "priority" (QoS) on VLAN traffic, so that someone playing World of Warcraft online doesn't slow down your 1080p streaming. Right around dinner time a new temporary QoS rule comes into effect making WoW unbearably slow. Now my kids come down from their rooms and ask when dinner's ready. Internet access is cut off automatically at 11PM, Sun-Thu.
VLANs solve lots of problems.