Welcome. The key to successfully getting a tank up and running is in your own post - "Will be building things up slowly".
Think about what sort of look you want.
Do you want lots of live plants or a rocks-only look?
Do you want a good number of small fish darting about or a few larger ones cruising by?
Are you thinking tropical or cold water?
Freshwater or marine?
Read up on how to cycle a tank before you start buying anything. By "cycle" we mean building up the good bacteria in your filtration system so they will neutralise the bad stuff that will grow in an enclosed system, like your aquarium.
Ask all the questions you like. As said, we aren't trying to sell you anything!
Whereabouts are you? If you go the User Control Panel you can add your location to your profile. There is possibly someone near you, or an active fish club, who can help you start your journey into fish keeping by offering hands-on help, or some established media from their filter to help your tank cycle.
Don't forget to use the search function as you may find many answers in previous posts as someone will have asked the same things!