You can start a topic sentence any way you like. A topic sentence makes a statement (or asks a question) the rest of the paragraph explains or gives examples of what the topic sentence has said.
For example the topic sentence is:
New Zealand is an island country in the south-western Pacific Ocean.
We would expect this paragraph to give us some more information about New Zealand, maybe about it's size, how many islands, the islands names etc.
So the paragraph could be:
New Zealand is an island country in the south-western Pacific Ocean. It comprises of two main islands the South Island and the North Island plus numerous small islands. The land area of New Zealand is 268,021 square kilometres. New Zealand's closest neighbour is Australia.
So your topic sentence can start anyway you want, it all depends on what your paragraph is going to be about.
It is the first sentence of a paragraph which is the topic sentence.
the first sentence of the paragraph is called the topic sentence which should describe most of the paragraph for the reader to understand. The topic sentence is usually the first sentence of a paragraph. It makes a statement (about a topic) and the rest of the paragraph explains the topic sentence or gives examples of the topic sentence. The second sentence of a paragraph can sometimes be the topic sentence. Sometimes it is called a summary sentence.
No, a supporting sentence supports the topic sentence.
if a paragraph does not have a topic sentence then
The sentence that states the main idea of the paragraph is called the 'Topic Sentence'.
Final.
A topic sentence is a sentence that explains your topic.
A topic sentence grabs a readers attention
The sentences that restates the topic sentence.
if a paragraph does not have a topic sentence then
Generally the topic sentence is the first sentence of the paragraph and the rest of the paragraph explains or gives examples of the topic sentence. The topic sentence can also be the second sentence of the paragraph. This is when the first sentence is a linking sentence that links the paragraph to the previous paragraph. Sometimes the topic sentence can be the last sentence in the paragraph
A topic sentence and a transitional sentence are not related. A transitional sentence moves the reader from point to point, each which supports the main argument or topic sentence.