The phrase "and only the first" is correct and usable in written English.
It can be used to specify that something applies exclusively to the initial item in a series or list.
Example: "You can choose from the options provided, but you may only select one, and only the first will be considered."
Alternatives: "just the first" or "exclusively the first".
Once triggered, the seizure exhibited a lower intensity, and only the first component (paroxysmal activity) was evident.
We were unable to determine why our LED's were not working properly and only the first five LED's would light up.
The first three seeding dates were the highest yielding in Los Angeles and Osorno, and only the first seeding date was significantly higher in seed yield in Gorbea.
The reduction proceeds in two distinct steps, and only the first step in the case of [Re2Cl8]2− is a reversible process.
But the move means space inside overhead lockers is in greater demand, and only the first 90 passengers are guaranteed to have their luggage placed in the cabin.
The program itself is financed through a federal grant from the 21st Century Community Learning Centers program, and only the first year of funding is guaranteed.
Aristotle's authority gave way very slowly, and only the first of the great scientists mentioned above did his work in the period under consideration.
The orally administered option, Grazax, a pill placed under the tongue, must be taken once daily and only the first dose needs to be administered by a specialist.
With all the deaths, and all the people who lost homes, I felt lucky: the family was safe, and only the first floor of the house was ruined.
AMC broke the season into two parts, and only the first half was televised before the May cutoff date for Emmy eligibility.
Ireland have of course had to deal with their best players seeking to further their careers overseas, with Joyce, Rankin and Eoin Morgan all pursuing international careers with England and only the first two returning since.
