There are many more Gaelic speakers than 5k, especially if you consider all the Gaelic dialects...
I'm specifically addressing Scots Gaelic. Irish Gaelic has a much larger body of speakers and LOTS of dialects. I started into Irish Gaelic and found a mix of dialects being offered inside a single Duolingo course. Another source of Irish Gaelic instruction comes from Molly McHale on Youtube "Gaeilige i mo chroi". She speaks Ulster dialect. Duolingo is using Munster and Connacht. An Irish Gaelic page cites about 23,000 Irish Gaelic speakers in the Gaeltacht zones of Ireland. For Scots Gaelic Youtube instruction, Jason Bond has very good instruction at "Gaelic with Jason". Good principles easily extended.
A Scots Gaelic page cites about 58,000 speakers of the language in Scotland today.
There is a web resource for learning Scots Gaelic. It is found at Learn Gaelic. It is a different approach from Duolingo. I should make an account and plow my way through. The first unit was pretty well done.