Expand Singapore into Jahor and Ethnic Chinese are not going to make up the majority of the population; which is the whole reason for Singapore breaking away from the Malaysian Federation anyway.
I'll address this first- the highlighted area is mainly the city of Johor Bahru which is currently 41% Chinese and 44% Malay. Historically the Chinese population was actually a bit higher. The rest of the highlighted territory is oil palm plantations and fishing villages. Demographically, incorporating that territory doesn't really change anything for Singapore.
First of all, is this plausible the following map below and with the two following additions;
1. Is it possible for this expanded Singapore to have a population greater than 10 million by 2010 with a POD of 1900.
2. With this expanded territory can Singapore maintain a large european population?
3. Another major city like Singapore or two?
As for plausibility, it takes quite a bit of doing-
First of all, that rather random slice of Batam is a bit weird. If anything's going to be incorporated the whole island would be. Doing that, however, is a bit hard because the Anglo-Dutch Treaty of 1824 puts the dividing line of influence between Britain and the Netherlands right between Singapore and the Riau Islands which is why the Malay cultural sphere is split politically the way it is.
Secondly, that slice of Johor takes some doing- Britain got the rights to Singapore because the then would-be Sultan of Johor ceded it in perpetuity in exchange for British support of his claim to the throne. He then set up his court in Johor Bahru, although the Sultans of Johor still maintain a residence in Singapore. Johor was never officially ruled directly by Britain- the Sultan took his 'advice' from a Resident while Singapore (along with Penang and Malacca) was part of the Crown Colony of the Straits Settlements. I'm not sure where the justification for taking more of the Sultan's territory would come from.
It's not that plausible. In fact incorporating the Riau Islands is probably more plausible- just have the Anglo-Dutch Treaty include Riau in the British sphere and have the Riau Islands become part of the Straits Settlements.
However, handwaving everything here's my take on your questions
1) Maybe. Singapore currently has a population of 5 million and IIRC the target by 2020 is 8 million. 10 might be possible.
2) I don't know what you mean by major European population- the European population was never particularly high and when the colonials left the MNCs took their place. I doubt the proportion of Europeans in the population ever really fluctuated that much. If anything it might be slightly higher now since white people have begun to actually come here to live and take up citizenship and raise families.
3) Highly unlikely. Basically you'd see Johor Bahru as a commuter suburb of Singapore (which is already the case to a certain extent). Again, as with the current situation, you would see industrial towns and resorts developed on the Riau islands but all revolving around the central city of Singapore. Basically like OTL except within the same political boundaries.