Hi Teenybash1980, I sense you don’t live in Donaghadee, otherwise a visit to the St Patricks Church of Ireland or 1st or 2nd Presbyterian Church etc could solve a lot.  You only have to find a couple of generations and you may find you link up to existing trees connecting to the 1901 or 1911 census which will be so useful for you. and if you stay interested then as you get deeper into it you may help them in return. 
I made notes, finding my earliest references from Ros Davies website start with
John NELSON . {b before 1773}  Donaghadee  leased land in Donaghadee in 1789 from Mr Delacherois FR
William NELSON . . {b before1773} Donaghadee  leased land in Donaghadee in 1789 from Mr Delacherois FR
she has much more
then 
seeking Donaghadee or Ballycross District
1834 Tithes Applotment books
from 
http://www.irishgenealogyhub.com/down/tithe-applotment-books/donaghadee-parish.php#.Vp1gJUvBEYUNelson, Frans. Townland: Donaghadee Year: 1834
Nelson, Robt. Townland: Ballyhay Year: 1834
Nelson, Robt. Townland: Ballynoe Year: 1834
Nelson, Robt. Townland: Donaghadee Year: 1834
Netson, Robt. Townland: Donaghadee Year: 1834 transcription enumerator error?
1863 Griffith-Valuation from 
http://www.askaboutireland.ie/griffith-valuation/Nelson    John        Down    Donaghadee Carrowdore
Nelson    Jane        Down    Donaghadee Shore St Map Ref 99 Plot18    
Nelson    Jane       Down    Donaghadee Warren Rd 99 5        
Nelson    Andrew    Down    Donaghadee New Road  99 4       
Nelson    Sarah        Down    Donaghadee Church Lane 99 7        
Nelson    Jane        Down    Donaghadee Meeting House Street 99 26;27   then 
1901 census 1911 census which give addresses and most importantly relationships too bulky for copying here 
I picked through familysearch, emerald ancestors and ancestryireland finding very few Donaghdee.  Sometimes bmds are registered in Newtownards and Belfast rather than Donaghadee
I believe a split approach in your time immediately, is your best plan eg one hour certificate finding, one internet hour checking for shortcuts in case they exist.  Seeking has anyone done work on your family or preferably your family name in one small location say a civil parish like Donaghadee.  if you haven’t found same named people in the area after a short time, try it again say once a month. Accepting and even checking somebody elses work still leaves you filling in your own knowledge and what you gather and possibly discovering their errors etc.
I have just one paid subscription to a family history website, which is GenesReunited { £44.96 GBP for a 6 month Platinum membership and extra payments for certain details.}.
 I entered its search engine for Nelson Donaghadee and to my astonishment the result was list of 92 entries covering births between 1781 and 1997. Many are the same person duplicated with different tree owners. A rough estimate is more than 50 different individuals are listed. These entries are in trees belonging to 23 members, the largest tree being that of a member called Shirley. To see her tree or any of the others you would need to join for six months.  The no means you don’t need prior contact before asking that tree holder for permission after you join up.  I cant do that for you.
edited sample  for ‘Hugh’ to 1935
Hugh   Nelson   1852   Donaghadee, Down, Ir...   No   Rose Ann
Hugh   Nelson   1882   Donaghadee County Do...   No   Shirley
Hugh   Nelson   1890   Donaghadee County Do...   No   Shirley
Hugh   Nelson   1932   Donaghadee County Do...   No   Iain James Mackenzie
Hugh   Nelson   1932   Donaghadee County Do...   No   Shirley
so Hugh Nelson 1932 might b one of the crew Hugh Nelson jr
Sometime go on the internet and find 
www.nelsonsboats.co.uk/contact-us/ make one phone call or send an email to Quinitin Nelson in case he has already the family history you want.  You will find he is a 4th generation Nelson associated with boats in Donaghadee.   Before you do so, I would advise you to clarify your information if you can on your mothers side because I couldnt work out whether Rachael Nelson being someone of the same maiden name or a Rachael x who has married a Nelson  
In case it crops up The Sir Samuel Kelly lifeboat crew members in 1953 at the time of the Princess Victoria disaster included six Nelson, out of  ten ie Hugh Nelson (coxswain) Alec Nelson, Frank Nelson [b1910] , Hugh Nelson Jnr, Samuel Nelson William Nelson plus James Armstrong, Samuel Herron, George Lindsay, John Trimble. All would be living in or very close to the lifeboat station. That crew saved 36 of the 44 survivors. Astonishing bravery. But you need to find the right one if indeed your Nelson was a crew member at all.
However you recently asked about Sarah out of the blue I presume you meant William George Nelson daughter and you were lucky enough to have a reply from a new member Shirleyc153.  That name is a name associated with the above website Genes Reunited.  Shirleyc153 is very welcomed anyway but if she is also the GR member you are very fortunate to have an experienced family historian on board. 
I stop here.