Realistically, you are better off going for the KBAC. I'll try to explain why I think this so that you can see whether my reasoning is applicable to your situation.
If you need to ask the question, it seems fair to assume that you do not currently have the knowledge/skill/experience to be comfortable doing it yourself. As with most things, doing it yourself will help to provide the knowledge/skill/experience, but you need to weigh up whether you are better off spending the time on this, or using your grinder and developing your grinding skills. Only you can decide.
I have bought cheap drives and mounted them in IP66 panels (the European equivalent of NEMA4 ingress protection) with a remote control box for start, stop, fwd/rev and speed control. The first few IP66 panels came for free and there was a saving over buying IP66/NEMA4 drives. I've done a few more since and, with the cost of the panel, there is no noticeable cost difference between my setup and the factory one.
In its favour, "my" solution has the remote control box on a 3M/10' long lead and has a 3-phase socket so that I can plug in any one of several machines and run them using the remote control box.
Also, if I fry a drive, it'll only be a cheap one and the rest of it will be reusable.
Some of the drives I have are "Sensorless Vector" drives. These can run motors smoothly at lower speeds than V/Hz drives and this allows me to run 2-pole motors (3600 RPM at 60 Hz) at very low speeds. All of the NEMA4 drives I have seen have been V/Hz drives. All the V/Hz drives I have used have been fine running down to about 10 Hz, but start to feel "coggy" when taken much lower. 10 Hz on a 2-pole motor is around 600 RPM. I prefer to run 4-pole motors (1800 RPM at 60 Hz) whenever possible. 10 Hz on a 4-pole motor is about 300 RPM. I run the 4-pole motors to 120 Hz maximum for around 3600 RPM.
I have a near-unlimited supply of 3 HP, 2-pole motors for free, so the SV drive is useful to me.
Against this must be balanced the greatly increased size: as you have surmised, the drive itself is air-cooled. There needs to be space inside the enclosure to allow air circulation to cool the drive. There also needs to be enough surface area for the heat generated inside the enclosure to be transferred through the enclosure walls to the outside air. It's not too much of a problem in North-West England, where I don't really need to consider ambient temperatures much above 70 degF: it does get warmer than this, but infrequently enough that I'll probably be out enjoying the nice weather instead of in my (hobby) workshop. I use either 12"H x 12"W X 8"D or 16"H x 12"W x 8"D steel enclosures for 3 HP drives. The enclosures are steel because GRP or polycarbonate would have poorer heat transfer, and have glass front panels so that the drive display can be seen.
Unless you have A/C in the shop, you are likely to need bigger enclosures in warmer climates.
The big enclosure needs to be screwed to the wall, preferably with the display visible from the machine it runs.
Putting the drive in the enclosure means you have no access to the front control panel and must therefore arrange to control it some other way.
The remote control boxes I have built for this are fitted with industrial pushbuttons for start and stop, a speed control potentiometer and a keyed forward/reverse switch. The Start button is flush with its bezel and must be pressed with a finger (or a stick). The stop button is projecting so that it will stop the drive even if it is slapped or flailed at wildly. The keyed Fwd/Rev switch has the key removable only in the fwd position and can be removed if it is running a machine that cannot safely be reversed.
The speed control potentiometer is generally whatever I can get that provides good quality at reasonable cost. Mostly I have used Bourns or Vishay 10-turn pots and knobs bought off ebay, but I've salvaged a couple of industrial single-turn pots, badged AutomationDirect, that match the industrial pushbuttons and they have spoiled me; using 10-turn pots is now just too much faffing about.
The way I have done it uses all industrial parts, engineered to standards that mean all I have to do is put them together competently in order to be sure the dust and water protection will be adequate. Cost is high but risk is low.
There are plenty of guys on the forum who have put together some means of protecting their drives from grinding dust without spending very much at all. One of the ways to reduce costs is to use an enclosure with a fan that provides a flow of filtered air through the enclosure. This deals with the heat transfer issues at a stroke, freeing the way for much cheaper boxes. If you engineer your own system like this, you are carrying the risk in exchange for lower cost. You need to have a pretty good grasp of the issues and this takes us back to paragraph 2.
