I have my gearing at 46x16 now but I know I need to come down if I'm going to ride 800miles on a single speed with about 30lbs so should I get a bigger free wheel or smaller chain ring? What sizes?

800 miles? Awesome! I think around 65 gear inches is a good starting point. Just easy enough to make it up most hills without spinning your legs off going down. I think there was a discussionin the long-distance forum about gearing for long distane fg riding, and everyones average came out to be around 65". Your 46 tooth chainring paired with a 19 or 18 tooth cog would be ideal IMHO.

What kind of bike and gear are you gonna use?

get an 11-34 freewheel.

Run a double stepped hub with 65 and something in the middle to low 50 gear inch range (and be prepared to suffer a little) and ignore anything Adriano says.

I toured on 44/16 and that worked out all right. Maybe try to be a bit aware of the days terrain and carry 2 sprockets. On tour sometimes you climb for 3 hours. If you know you're gonna be doing that swap gears, swap it back when you get to the top. It should only take a moment to do this. When I toured fixed I just used 44/16 on its own.

that's a great idea. A flip/flop hub with a easy and easier cog or an uphill and downhill cog would work out great. Don't forget about the surly dingle cogs too if you run a 3/32" chain.

What I have is an SE frame but it turns out its not a bad bike once you replace all the components