Welcome ikwokon
You will probably get a fair variety of recommendations, because, there are so many ways to do macro. Recommendations will range from cheap to expense, easy to implement to hard.
The camera you have is very capable. I would be thinking about the camera first before the lens. Firstly, the ISO performance is good, but not as good as current models. Shooting at up to iso 800 is ok with the sweet spot being about iso 400. I suggest this as it is a good compromise between noise and speed (light will be an enemy in macro as you will come to learn).
The onboard flash is ok. A cheap upgrade is the acquisition of a hotshoe mounted diffuser to soften the flash light - this will vastly improve your flash macro work. Alternatively, you can get a really good mounted flash such as a Metz 58 II .... but the expense is high and perhaps too much for your stage.
So now to what mode to use. That will partly depend on what lens you get (manual, AF, 'A' contacts or not, M42 ...). Without confusing the matter you are probably best going for a K mount with 'A' contacts at the very least - AF is not essential in macro so don't sweat it on that level. This means you can control the aperture with the camera body. More advanced is a fully manual lens where you will have to use the 'green button' (ps unless you are familiar with this I suggest not thinking about this at this stage). If you get a 'A' lens then you can use P or Av mode with ease.
Now for the lens. Assuming you are using a 'A' lens then you need to contemplate focal length. Insects are fussy and react to lenses taht need to be close to the subject. So, othar's recommendation is very sound. If you have a spare $400 then go for the best - I suggest here a Tokina (aka bokina) 90mm 2.8 with 1:1 adapter. NICE. A Tamron 90mm f2.8, with different optical formaular is also very good at a slightly smaller price (say $250). Alternatively you could go for the Pentax A 100mm f4 - not a bad option but it is not a true macro (2:1). Another very fine lens is the Vivitar Macro 'series one' A 105mm 2.5 for about $300. In any case you are probably looking at about $300 for a very good quality manual 'A' lens. Otherwise, you could buy a FA100/2.8 macro for a similar price or even less - a marvellous lens with the added feature of AF.
Anyway, you really can't go wrong with any of the lenses mentioned above, it will just depend on your price point.
Have fun
---------- Post added 29-06-17 at 09:22 PM ----------
very capable lens
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