a piece of advice -- buy any seconhanded DSLR camera, they can be comically cheap! Pentax or Sony may give you little benefits in the long run (imo). I stick to Canon and to my lense park i've already got, otherwise i'd change it... if you're not limited - buy modern mirrorless Sony or Fuji camera with changeable optics.

when you have a camera, buy a 50-mm lens - there are very cheap, too. It can be your everyday universal lens. I cant talk for other systems, but Canon 50mm 1.8 is very, very cheap. also, having a DSLR camera, you are open to use a very big park of pre-digital lens, they will not have autofocus (i.e. you have to focus manually) but they are cheap! well, some of them. in comparison with modern AF models, they are really a bargain.

so, you will get fun already on this stage.
if you're not going to restrict yourself to macro, using 50 mm lens and taling shots of various stuff will show you what you like to shoot most - and what lens (i.e. typical focus ) you will need to have in your arsenal... getting a lens park is a long venture, that can be a lot of fun (and a lot of investements, hehe)

next is getting lens for macro. 1st thing to know - the closer you can get to it, the bigger will be the shot :) you know that already. 2ndly: you dont need auto-focus for shooting macro, 99% of time you better go manual. so, assume you dont need expensive AF lens (which are better), but you can go with old, outdated, but still great manual. soviet lens 'Industar' (a replica foof german Zeiss Tessar) is a good and not very expensive macro lens, for example.. there is a lot of self-made macro lenses out there. you will just need to choose :) I have two AF lenses in my pocket, 60-mm Tamron and 150-mm Sigma (I use them on different cameras). If you can spend a bit more on this, I'd recommend you Sigma 105-mm AF - there are Nikon and Canon versions, and probably more; my friends on steem are getting great results with the Nikon version. If you can invest into it like crazy, and your girlfriend/wife will support you -- then, Canon EF 100mm f/2.8L macro IS USM is a killer. I tested it and fall in love. but it was completely out of my budget.

i dont recommend you getting anything more than 105-mm lens. its not handy, you will need tripod with it... mostly impossible to get decent results.

will be more questions - ask.. @macchiata, i'd appreciate some piece-of-cake curation too.. recently I'm shooting dandellions, thru the summer will be doing more macros, like this.. you may keep an eye on me?