Hi
A tourism portal. Is this going to generate an income? If so it is likely that it will be centred around accommodation and visitor attractions.
Different types of accommodation have different priorities - hotels, guest houses etc charge by the night; self catering by the week or short breaks - maybe a minimum length of stay and maybe a start date.
Then there is on line booking, a large number of establishments now have their own systems and it is very difficult for a small business to operate more than one. The simplest system is to provide a link to the owners booking engine but this does remove a revenue opportunity.
Trip advisor links are becoming very popular.
Are businesses going to have access to the site? Will you have "offers & late availability" pages. I think you are right in saying that you need advanced search/filters. You might feel that is is appropriate to list businesses randomly but to maximise an income you might want to list them by such criteria as availability or grading.
Is the idea behind the site to keep the visitor within the site or to provide links to business web sites.
K2 will produce a site but you might want more flexibility there are joomla extensions for both real estate and reservation systems which can be found here.
extensions.joomla.org/extensions/vertical-markets Of course accommodation might not feature on your site in which case the above is not very helpful!
Regards