Those coming from the west of Finland typically have Swedish-Finnish surnames, with those coming from the east of the country have origins inline with Latvian or Estonian descent.
Finland gained independence from Russia in 1917 and it was in 1921 that legislation directed everyone to have a surname. Up until then people just used their given name as their communities were generally small.
Once mandatory surnames was introduced, many chose surnames that were occupational names. For example, Suutari is Shoemaker.
There are also plenty of Topographical surnames, generally indicative of where someone was living, for example – Aarnio means pristine forest. As many people chose this option the use of suffixes and prefixes became necessary. Those that lived higher in a community (up a hill for an example) added Yia or Yli to the end of the name. Those that lived lower down the hill or valley added Ala or Ali
The most common suffix is that of nen, originally indicating someone was from the east of Finland. It quite literally means small, though sometimes it is used to mean son, for example – Hanninen, Small son of Jonannes. On occasions the name refers to the place the family originated from, for example Ahonen means small forest glade or clearing.
The second most common name in Finland is Virtanen meaning small stream or river, and was often used by families whose settlement was literally near a river. Further exploration could be to explore the rivers in Finland to gain an understanding of where those rivers were, the topographical details of those places and then to drill down further to see if the place is a reasonable starting point for research.
Hamalainen was the surname adopted by those who came from the Hame district of south west Finland, north of Helsinki – a Topographical name. The surname of Heikkinen is means son of Heikki which is the equivalent name to Harry, meaning ruler of the estate, or household. The potential is for this to be the Finnish equivalent to the son of the Lord of the Manor – a Patronymic name. The name of Jarvinen which means a small lake indicating a family that lived close to a lake. It might be a tall order establishing which lake, Finland has 188,000 lakes! Again this is a Topographical surname. Laine is the Finnish word for wave or ocean, suggesting a family originated from a coastal area – a Topographical surname. An alternative could be a Characteristic surname – of someone who laid back, essentially going with the flow. It is a different spin on the surname, and whilst I would not discount it, I would opt for the first meaning.
There are approximately 24,000 surnames in Finland with a population of 5.5 million. The image below is a population density map which is identifying the spread of the population across the country. The darker the colour the more population there is living in the area. Whilst it is not an absolute way of working on your Finnish ancestry, it gives you an idea of the location of places in Finland and how densely populated a place was, thus providing context to your research.