There should be no issue pulling a siphon over that distance. I just built a 420 gallon dual system for a friend with a full siphon over 20 feet. I'm doing the same at my house at the moment at greater lengths
Cully has a good point on water flowing back to the sump. If you look at my V2 upgrade thread I calculated the volume of water in the full siphon lines, and it adds up!
http://reefcentral.com/forums/showthread.php?t=2109690
If you go full siphon make sure to use gate valves.
I also aim for 5x turn over from the return pump, though you can go to 3, aim for 5. this should be coupled with good powerheads so you get a good turnover within the tank of at least 20x for SPS
The plumbing size - yes, size matters. it has to do with the friction on the edge of the pipe, the smaller the pipe, the harder it is to get the water through. If you size properly you get more flow which could mean a smaller pump for the same effect (lower recurring electric cost). you can somewhat cover this with a pressure biased pump, but that usually means more electricity
your tank is a 150 so we will aim for a flow rate of 750GPH
7 vertical and 10 horizontal with (4) 90 degree bend
using RC calculator:
http://reefcentral.com/index.php/head-loss-calculator
Note:
(1) I pulled the prices from dr foster and smith, there are cheaper places
(2) I personally am moving away from Mag pumps, I used the example to show the significance of proper plumbing
to get 705GPH on 3/4" pipe you need a MAG24 ($242)
you can get 675GPH with a Mag 12 if you use 1" piping ($171)
you can get 797GPH with a Mag 12 if you use 1 1/4" piping ($171)
so you can get 92GPH more from a pump that draws less power and costs $70 less by using 1 1/4" instead of 3/4"
If you need to go through a tight area for the siphon or return, reduce it and bump back up, yes it will affect the turnover, however it is MUCH better than running a smaller diameter throughout.
In your case I would look at a 1 1/4" for the return, 1" for full siphon (forgot the number, believe it is over 1500GPH on full siphon on a 1" line), and a 1 1/2" for the regular drain.
for an external pump I would consider (in no order) - Nate knows his pumps, he can weigh in on which are better than others. I put a * next to what I would look at
785GPH - blue line HD 40x
700GPH - Iwaki 40RT-2
* 993GPH - Iwaki 40-RXT-2
728GPH - little giant 4 MDQ
* 936GPH - MDQX
* 955GPH - Gen-X Mak4
Reeflo Dart (not in the calculator - should be around 700GPH)
internal:
quiteone 4000 High Head (haven't used this specific one, but I have been enjoying my quite one pumps, very easy to service)
(I left the Mag off, because I'm just not impressed anymore)