Hi there,
without taking what I say as being totally exact, in general a town house is a house that probably does not have a proper garden, maybe just a court yard, and access to the front of the house is usually very close to the street, or on the street. They are usually joined to another house or building on both sides, but can sometimes be free standing, meaning totally detatched, so there is no 'rule' for attatched or not. They often do not have a garage or parking.
A terraced house could be very similar to a town house, except that it would be in a row of houses that all look the same and are always attatched on both sides, which means that there is never a garage joined to the side of the house (but there could be one around the back). The exception to the attatched 'rule' is an 'end of terrace' house, which, as the name describes, would be at the end of the row, therefore attatched on one side only.
A town house is usually a 'one off' and can have lovely, original features and an unusual shape, and sometimes quite an agreable living space once inside.
A terraced house usually looks like all the other houses on the row and often holds less surprises once inside than some town houses can.
Your first feeling, that terraced and town are similar, is basically right, though when talking about the practical side of things.
A maisonnette can be harder to describe because it is one of those wonderful French/latin words that has been transformed in more modern times to describe something that didn't really exist up until recently. So, as a general rule again, a maisonette is usually a modern type house within a 'block' of either houses or apartments;
the maisonnettes I know share private parking lots with the maisonnette neighbours, but have their own front door, which doesn't make it an appartment. I know some maisonnettes with small private gardens and some with no outside space at all.
"Converted" often just means renovated, but it could also mean that a house with a lot of volume has been "changed" into two or more smaller living spaces. For example, a large house with an upstairs could have been "converted" into a ground floor apartment and a first floor apartment, each with independant entrances and living spaces.
I would hope that any property advertised, whether for rent or sale, has electricity and plumbing installed, otherwise the person could be breaking the law by not stating otherwise, so don't worry too much about the word "converted." In literal terms, it just means "changed into"...
It is also a way to say that the residence still has original features and has not been damaged by over modernisation over the years.
If you like 'modern', look at maisonnettes; if you like 'originality' and independance, look at 'town', and look at 'terraced' only if you come across something that really looks like the visit is worth it.
I know that things are so different here than the States so I do hope that this has been of some help,
Good luck,
LI.