I know I'm not the most experienced builder on Cohost, so I'll tag this in case anyone else wants to chip in.

Gunpla should be a good starting-point: I hadn't touched plastic models for decades, and never solo, before I got started with gunpla. Caveat: basic or intermediate gunpla building, of the sort I do, might not give you experience with all of the things that Maschinen Krieger models might expect. I've never built one, but e.g. those might be where you'd be getting into weathering effects, serious glueing and cementing, &c.

Tools

The absolute minimum requirement to assemble a gunpla kit comes down to just one thing:

• nippers

You can get an entry-level pair of plastic model nippers for not very much, and you can build a kit in full using just those. At each step, snip the parts off the sprue at the gates, nipping a little away from the part itself, then snip the remaining nubs off the parts, then assemble the parts, bang, model done. It won't look as good as something assembled with more care, but, seen from a distance on the shelf, a surprising number of its imperfections will pass unnoticed.

You might want

• a pair of tweezers with curved ends, to help with applying stickers.

Most people fairly swiftly find they want to do a neater job cleaning up the nubs left on the parts, for which, as I understand it, the commonest tools are

• fancier nippers

  and/or

• a modeller's knife

You can get more expensive pairs of nippers which're specialised for snipping the nubs off—so specialised that they don't like having to do the brute force work of cutting pieces off the sprue initially. Or you can use a sharp modeller's knife for the same job, which in some ways gives you more fine control, but can also rip the plastic rather than cutting it if mishandled or blunted.

To do even more to smooth out nub points, some people use, e.g.

• a set of graded sanding and polishing sticks.

The other next-step set of tools that springs to mind is

• one or two panel lining markers

Someone wrote a helpful post on this topic on here yesterday which I recommend. I, personally, like to have a grey panel liner for pale/bright pieces and a black one for other pieces, plus some cotton buds and my fingers for wiping off excess. It's something I find satisfying and it does add a bit more visual 'pop' to the model.

I haven't yet experimented with

• coatings, primer, topcoat &c, or paint.

Remarkably, even more complex gunpla usually doesn't require glue; I've only used plastic cement when I broke a part, once.

Kits

Off the top of my head, I'd suggest starting with a 'High Grade' (HG) kit. Despite the name, most of these are pretty welcoming and will deliver a good-looking model in not very much time. If you're really uncertain or you want to involve a younger child or something, there're also 'Entry Grade' (EG) kits which offer an even gentler build.

When I started, I was told that basically any HG kit from the last two decades would be fairly approachable and that, so far, has proved true. Kits from the last three years (or maybe a little more?) actually have bilingual Japanese-English instructions, and most of the Witch from Mercury kits I've built have felt especially friendly, but the 2003 HG Hygogg kit I did wasn't dramatically harder to understand or assemble. Gunpla instructions are very image-driven, and the few symbols they use can be googled easily ('gunpla symbols' usually brings up a cheat-sheet somewhere).

My only warnings about HG kits for an absolute beginner would be:

• maybe avoid the large, expensive end of HG, e.g. the HG Ξ Gundam: this is HG, but it's huge and costs, in UK prices, £60 or so. That's roughly three times what I'd expect normally to be paying for an HG kit, and the kit would be a lot of work.
• maybe avoid kits which are meant to transform, as that adds a lot of complexity; I was glad I had a few kits under my belt before I did the HG Zeta.

Otherwise, I think you can largely buy and build what you like! I started with the HG Gundam Mk-II, Titans colours, which came out looking great even though I was a total amateur, and the kit I did after that was the HG of the original Gundam, which was easier and also came out well.

The internet yields lots of helpful gunpla advice to careful searches, and with many kits you can find a video of someone building it on YouTube if the process becomes unclear at any point!