In answer to your questions:
1) The sidebar is not configurable from the ClassiPress admin dashboard, so it would require
customization of the default theme on your part if you wanted to change this. How "easy" it is, is ultimately relative to your level of coding knowledge, but yes it can be done.
2) You can disable the slider without customization, you can select the setting in the ClassiPress admin dashboard to disable it.
3)
a) You can remove all other countries, leaving only Singapore as the only option (no customization required), or through customization you could potentially make it a fixed field.
b) ClassiPress has a
custom forms and fields functionality, so you can either create a custom ad form (simply leaving out the "State" field), OR you could edit the "State" field and rename the title to something relevant to your country (e.g. Province), and also edit the field values to show locations relevant to your country. Either method does not require customization, this can be configured in the ClassiPress admin dashboard.
c) It is a core ClassiPress field, so is fixed to a text box by default. It could be customized if you wanted to change this, however you could also remove it from the ad listing form by using the custom forms function.
4) The theme does not offer this option by default (currently you can only use one language at a time), however there are changes planned for the next major release of
ClassiPress v3.3 which will allow compatibility with the WPML plugin. We have been working with the developers of the plugin to make it happen, and essentially we are creating a plugin specifically for this purpose which can be used with the next version of the theme in conjunction with their plugin.
Thanks.