There is a company called Ultimak that makes the best railed foregrips for the AK series weapons. The
fore-end rail is the only style, I suspect, that will work with that bullpup design.
The preferred setup on the AKs is to use the side-mount rail that is riveted to the receiver, but the bullpup won't allow that. Tapco also makes some, but is a step down from Ultimak. Neither are as good as the side-mount, but with the bullpup it isn't an option.
There are many red dot sights out, of course. Unfortunately, the ones that are markedly better than the rest are also much more expensive. Aimpoint makes a variety of high end sights, many used by military services (including the US and Canada). My favorite is the H-1. The advantages of the Aimpoint series is their durability and battery life. The H-1 has a battery life of over 5 YEARS at setting 8 (out of 12). That means you can turn it on and leave it on, so it's ready to go-all the time. It's also tiny and very, very quick. The Comp M4 is a bigger sight, uses a AA battery, and lasts 8 years (!!!) on a normal setting.
The other top-tier choice for this type of sight is the Trijicon ACOG. It is more of a "scope" albeit illuminated by 3 types of light sources. It may be tough to fit onto your fore-grip rail and get the proper eye-relief; it may work great.
Eotech makes super cool sights, and they break more often than the others I mentioned under real use. (Military and police service, where they get bonked and tossed around and into things, and handled a lot.) In comparison to the Aimpoint series their battery life is pitiful. Some prefer the reticle of the Eotech to the plain dot of the Aimpoint; in some trials I have read about the Aimpoint is slightly quicker.
If you aren't going to buy an Aimpoint, ACOG, or, to a lesser degree, the Eotech, most are all about the same level of crappy. I'd buy one from the local retailer that has a good return policy. TruGlo is probably the top choice of the lower end products. It's actually a decent sight in its own right, and I've got one on a rifle of my own.
Don't buy anything at a gun show. There are a lot of Aimpoint, ACOG and Eotech branded knockoffs, that are extremely similar to the real thing in appearance, but don't have the quality or the battery life. Only buy these from an authorized dealer. Gun shows are notorious for having products like these for sale. Even if the seller isn't aware of it, they are still ripoff and low quality products. Just buy the TruGlo instead of these knockoffs.
I wouldn't mess with any of the off-brand red dots either. The top end products are literally lifetime purchases of hand-me-down quality, that grandchildren will be able to use and enjoy with grandpa, and pass to their kids, and the TruGlo may last as long too, and isn't significantly more expensive than the cheap ones.
For a serious "truck and tractor gun" the AK or AR are both good choices. Put an Aimpoint on either of them, get some good magazines and ammunition, and shoot them as much as you can afford. For the AK anything foreign made is generally better than the American ones. For the AR, Pmags are the best. Otherwise, get GI magazines with the upgraded followers. Shoot several loads through each magazine, too. Fix any that don't work right by putting them under your tractor tire and driving back and forth across the top of it.
One more thing: Century Arms AKs have been, in the past, hit and miss as far as quality. Some are superb, and others are terrible. Bullpup conversions of standard configuration rifles are the same, and are known for poor triggers. Make sure your dealer is a standup guy and do a detailed inspection of the weapon before you take it. (One of the common things was/is for the front sight to be pressed on crooked!) Make sure to shoot it a bunch the first week or so you have it, and make sure any bugs are worked out early.
Last, take pictures so we can see what you get, and how you carry it on the Kubota!