Yep, measure twice, cut once.
Other things to take into account are that the throttle, gear & steering cables all have minimum bend radii, unlike the rope. You might want to use the current cable to sanity check that. you may also find that you can use the old ones - I don't know how your current setup is, but unless you are using under deck trunking, the line from the throttle to the engine on a centre console setul is pretty much a straight line. If you have a slightly convoluted route at the moment you may be surprised how much extra you have hiding in there.
When positioning the throttle, remmebr that it not only needs to be useable at idle, but ideally wants to be in a comfortable position at WOT. If you do a lot of cruising, you may find mounting the remotes at a "funny angle" gives a more ergonomic position. (Mine the lever is at about 20 degrees to horizontal at idle - puts the lever right at my fingertips when standing, and misses my knee nicely at idle. Also puts it right on
my knee in reverse, but for a couple of mins whilst manoevering, so I can live with that.
Another thought for the pot: I stand a lot when driving, so have moved my remotes a bit higher than normal - one simple reason - having the throttle that extra 6" off the floor means I can stand and reach it comfortably. It's a little high when sitting, but on a par with the wheel. Always worth a double check before you drill.
If you think you'll be buying new toys (plotters, replacing your Icom 421 with a 503 witha bigger case etc) remember to reserve space for them too.....