Sedna, space probes?, colonies? what's next?

I find it interesting that Sedna was discovered near its closest point in its
10,500 year orbit around the Sun. What are the chances of that happening? If
you only consider the planet Sedna, the chances of discovering it while it is
near is closest point to the Sun are very small. Sedna spends most of its time
further away, this leads to the question how many other "Sedna's" are there?
What if we looked for a 10th planet 1000 years ago with the same technology we
have today? Would we find another Sedna-like planet nearing its closest point
to the sun. Sedna will spend 150 closer to the Sun than from where we
discovered it. statistically this leaves room for about 60 planets in 10,000
year orbits around the sun. all those planets are potential colonies for future
colonists. The ones further away will be harder to find, but I'm sure we can
eventually discover them.