Well, the siphon should be on the 3/4" bulkhead in the first place. This is a basic "safety" concern in that the siphon be placed on the smallest bulkhead, and the emergency be placed on the larger bulkhead
Second, you do not need a valve on the dry emergency, nor on the open channel. Removing them will make running your pipe easier.
On this, the first thing you should do is reduce the number of threaded fittings in the system. Threaded fittings will always be at risk of leaking, and the fewer the better. Many want threaded fittings, so they can take the plumbing apart, but in reality, if the plumbing is done right the first time, they will never take it apart till moving the tank, or upgrading to a larger tank, and the plumbing will have to be re-done anyway.
It is not advised to use tape on threaded joints. Rather use a non-hardening thread sealant.
http://www.lascofittings.com/threads
https://www.customaquatic.com/estore/control/product/~product=PF-SPSB75-005
One of the largest problems with threaded fittings, is they are put together way too tight. Lasco provides instructions for the proper assembly of threaded fittings.
Also threaded unions should be avoided if at all possible. Every union is a possible leak point, and they are way over used in the hobby. Like I said before, the likely hood of actually taking your plumbing apart after it is finalized and the tank "live" is very slim to none. The only place they are acutally needed is at the return pump.
Horizontal runs can be unpredictable, one person will claim the system works fine with horizontal runs, others will claim they don't. I advise that they be avoided altogether, thus eliminating the variable, rather than guessing which way your system will go. In all cases, function comes before aesthetics, however, plumbing done right will seldom look horrible. It may take more thought, though. (Things such as sump design, among others.) These things should be worked out before buying/building a sump, or buying any parts for the plumbing system. It is easier to modify parts on paper than it is to modify a plumbed tank. The only way one gets painted into a corner, is by getting in a hurry, probably the number 1 problem in this hobby.