A hand held GPS can send position data to a fixed mount VHF. But I have heard that this violated FCC rules. Word on the street is you are supposed to use a fixed mount GPS.
I did not question this too much, as I have a fixed mount GPS and it is connected to my radio. I just said "OK whatever you say" and left it at that.
But in reality, no matter what the FCC may or may not have said on this subject, yea a hand held GPS is just as accurate as any other GPS. Assuming it can get a reliable signal where it is located.
I would say just get the fixed mount GPS. The screen is larger and you can load marine chart data into them. I have a hand held GPS that I carry on the boat, but it is a backup. The last time I remember using my hand held was while on my kayak at the Columbus Day madness that happens in South Florida. Finding your boat among close to 1,000 other boats all anchored in a small area is a lot easier if you have a waypoint to follow.
Connection is easy. Your radio will come with connection wires. So will the GPS. Connect them together and that is about all there is to it. Just remember that the data out on the GPS goes to the data in on the radio.
The dealer who you are paying to do the radio install should connect your GPS to the radio for you. It will take them all of 30 seconds to do this. There should not be any additional cost to you for this. Heck if you ask me the install should be free, you are buying a new boat and new electronics from them as it is.
When you get into DSC there are two types of radios. There is Class-D and SC-101. The cheaper radios are (mostly) SC-101. What this means is they are constantly scanning channel 70. If you are listening to channel 70 the radio will switch back and froth from 16 to 70. If you are receiving a transmission on 16 (or any other channel) then the scanning function pauses - meaning you can miss a DSC call.
Class-D radios have a separate receiver always tuned to channel 70. The only way you can miss a DSC call is if you are talking on the radio at the time the call is sent.
I like the Class-D radios. I actually use DSC. I have some friends MMSI numbers programmed into my radio and when I am on the water I send a group call. I also have the Sea Smart VHF thing going so I do not get constant phone calls asking me where I am. Nosy people can log into the account, send a DSC call, and my position shows on a map.
NOTE - I am not so sure Sea Smart was a good idea. I still get calls. I can't win no matter what I do.
The lowest price Class-D radio I know of is the Standard Horizon Quest-X. You can get it online for around $120 - $130.
I am a huge fan of DSC When I take non-boating friends I just tell them that if anything happens and they have to do is press the distress button. Thats it. So far nothing has happened that would require messing with the distress button