As far as gauges go … Analog is actually more accurate than digital … I prefer analog all day long … More accurate, easier to read at a glance, etc. But thats not here nor there.
Do you NEED a 150? … No … a 100gph will work … but the ONLY way to keep the lift pump in the tank is to put a new draw straw in, which will require dropping the tank. So you can ethier drop it and put the straw in, or drop it and pull the pump out. Pulling the pump will take less time & less work to be honest with you. The 100GPH does not REQUIRE a draw staw like the 150 does … but without the pump needs pulled.
Stay away from the K&N intake … There are GREAT for gasoline motors, but not so great for diesels. I have seen more K&N systems let debris in, than any other system.
I would go with a AFE Stage II (what I run) or a S&B system (they are cheaper than AFE). I can send you prices if you want.
Your not going to revive the LP … It is on its way out, and there is no stopping that.