Congratulations on the purchase the 175 Suzuki is a good upgrade over the 140 (which are much smaller engines than the 150/170's)
s not much difference with the 175 except at the high end over the 150's (due to variable valve timing, which only cuts in a high speeds). Not sure about what top speeds you want to achieve, but our 3 year + old boat still hits in the high 40's with cruising gear. You will find that most cruising will be in the 20 to 35 mph range.
As for lap top vs dedicated displays--I advocate dedicated displays. Especially if you want to go fast, you want to have the display just below your sight line thru the foreward windows. You don't want to be fooling with keys and mouses when working with the computer--dedicated keys of dedicated displays are far better.
The broad band radar-there are some excellent high defination radars which I would still choose over the Navico Broad band units. As noted the broad bands are best at close range--again at speed, you want at least 3 to 6 mile range. I don't know how much experience you have, but there will be a learning curve either way. If you want overlay on the chart, you will need a gyro rated fluxgate compass. Sometimes this is integrated with the auto pilot. w= Agree that AIS would be a good addition.
As for propane cooking--I have used it for many years on larger boats. Not on the C Dories I have owned. I have found that the Wallas stove is very adequate, if you understand how to use it for both heating and cooking. If you want to upgrade a heater, then go with diesel; not propane. The propane requires a large storage bottle for a relitatively small amount of heat--diesel is far better, plus much safer. Any open flame (propane) will cause moisture in the cabin. The Wallas diesel stove is vented to the exterior--and does not cause condensation--but of course boiling water of any heat source will cause condensation.
As for light--you don't need more in the foreward cabin. Changing out the ports would be a mistake. You have plenty of light from the hatch. In fact we put a shade under the hatch to keep the light out. You will get ventillation from the hatch--not the windows--even if you enlarge them.
As for the surveyor--some may find defects--but it will probably not be during a ride. Hopefully your dealer will take care of any problems in your boat--you might want to read my saga with repairs on my Tom Cat:
http://www.c-brats.com/viewtopic.php?t=3892&start=0 If you take the time to read this it will give you an idea of what to look for in potential defects. The place a surveyor should help is making sure that the boat is up to ABYC specs.
Also remember that a 2009 C Dory Tom Cat 255 will not have a factory warantee, so you want to make sure that the dealer will stand behind the boat incase of any problems.
As for brand of electronics--I would look very carefully at Garmin--although there are a number of other very good electronics. Garmin is the easiest to use, has some of the best cartography, and a good high def radar at a good price. Furuno is top notch, but a bit more difficult to operate. If you are willing to spend the $$ then go Furuno with a good HD radar. The best radars are not practical in a C Dory type of boat, since an open scanner of 4 to 6 feet is not practical. Don't worry about the radar emissions--you are well below the beam,, even with a low arch. Beside unless you are concerned about reproductive organs or eyes and will be directly in the beam, recreational radar, is such a short pulse and low energy that there are no heath issues.
