Is it necessary to start in class 9?

It is, because class 10 mathematics and science rest on class 9 concepts. But preparation now means the base and the habits, not suggestions.

Should I sit model tests now?

No — the syllabus is not finished. Model tests belong to the second half of class 10, once the whole syllabus has been read through once.

Which subject should I take first?

Mathematics and English, because gaps there affect every other subject and take the longest to fill.

SSC 2028 Two-Year Preparation

বাংলায় পড়তে চাও? দেখো: এসএসসি ২০২৮ দুই বছরের প্রস্তুতি

With two years in hand the biggest risk is starting nothing, and the second is starting the wrong thing — collecting suggestions or sitting model tests now, when neither has any use yet.

What class 9 is for

Find and fill the gaps in mathematics and English — gaps there hurt every subject.
Get into the habit of writing a summary in your own words after each chapter.
Write the practical notebook as you go; do not let it pile up.
Establish a fixed daily study time.

What class 10 is for

The first half of class 10 is for finishing the syllabus, the second for revision and practice. Hold that division and you arrive at the selection exam prepared, and it becomes the rehearsal it is meant to be. For students still finishing the syllabus when it arrives, it is not a rehearsal but another crisis.

What is pointless right now

Collecting suggestions — there is no suggestion for a paper two years away.
Sitting model tests — the syllabus is not finished yet.
Buying several guides — finish the classroom book first.
Hunting for a 2028 routine — it does not exist yet.

The habits that will last two years

The real foundation is not a book but a few habits — sitting at a fixed time, writing in your own words at the end of a chapter, collecting your errors in a separate notebook, and asking at once when something is unclear. Formed in class 9, those four halve the pressure of class 10, because by then no method has to be invented.