Low key is definitely NOT an easy way to start; learn broad & short lighting, masculine and feminine posing and other basic techniques. $2000 is ample. A decent four light, 800 w/s second used Speedotron Brownline kit will come in at less than $500. Stands, triggers, and a few reflecting umbrellas in various sizes should add another $500, leaving you ~$1000 for the single most important expenses: Licenses and insurance.
I think you want some "classic" equipment pieces, meaning light shaping tools. Speedotron's on-line catalog shows a lot of classical, light-shaping tools. Things like 7-inch reflectors, honeycomb grids for their various sized reflectors, barn door sets, scrims of metal screening, clamshell background reflectors, and their own brand of mylar diffusers which clip-on to their reflectors.
Light-SHAPING tools: grids, barn doors, snoots, diffusers, and different degree-angle metal reflectors; these are the things that make studio lighting with finesse possible.
Umbrellas and soft boxes are fairly basic, crude light modifiers. An umbrella throws a big swath of light. An un-gridded softbox throws a fairly broad light swath.
You want things that will allow you to place lights "just so", so you can add accents, rim lights, hair lights, etc, and do so from normal distances.
If you go inexpensive in Speedotron, buy a used, Brown Line
D402 power supply, and four, identical flash heads, like M11 flash heads. And then locate a Y-splitter cable as a handy accessory. This 4-outlet pack has a number of commonly-needed ratios, as well as a Symmetrical option, where the total flash power is distributed between
the number of flashes connected, at either Full (400 W-s), or at Half power (200 W-s) on the switch.
The D402 also offers an "Assymetrical" mode, in which Outlets 1&2 are high-powered, and outlets 3 & 4 and lower-powered. This is very useful, and has been worked out over decades of actual, in-studio use!
In Speedotron, 100 Watt-seconds is what many MIC lights call "300" Watt-seconds, or even higher.
If you buy modern, monolights, buy four identical, low-powered, 150-Watt-second units that have interchangeable 7-inch grid-accepting reflectors; these are often called "grid reflectors", and then buy at LEAST 3 grids: 10,20,and 30 degree. And buy a 2-way barn door set. And get some Speedotron 7-inch snap-on mylar diffusers. These can be stacked! 1,2,or 3 on a light unit!
With d-slr's, 150 Watt-second monolights are PLENTY powerful for most uses!
Speedotron Brown Line gear is plentiful and low-priced on the used market and is TOUGH...it lasts for _DECADES_,literally, it is NOT Made in China quality...it is bulletproof. But, it is simple. The D402 power supply is the easiest, 4-outlet pack to use (I have 200,400,600,and 1600 W-S Brown line and 400,800, and 2 x 2400 Black Line packs). I often prefer the power output options and the size and weight of the 4-outlet Brown Line D402 pack to the others for most portrait-type uses with ISOs in the 100 to 400 range.
Using 4, identical flash units makes accessory mixing and sharing easiest; being able to mount a 7, or 11, or 16,20,or 22-inch metal reflector on the M-11 flash unit, OR to use with an umbrella, or use with a softbox and speed ring, makes the M11 the best overall Brown Line flash head. Using 4, identically flashes makes it easy to get a WYSIWYG exposure preview, plus the M11's use a 150-Watt quartz-halogen modeling light, so it's super-easy to see and to focus, plus, if need be, some low-powered, 2-pin heavy-duty truck turn signal bulbs (25 to 35 Watts) can be inserted into the modeling light socket if you want to use the light with a snoot, or where it will definitely get hot.
The brand of "fit" or "accessory mount" is critical...Bowens S-mount, or "Bowens" as it is often called, is an excellent "fit". Speedotron Universal is what all Black Line and Brown Line M11 light units use.
Adorama now sells its Flashpoint monolights with the Bowens S-type mount; formerly, they used a very old, uncommon accessory fitting/mount. You want a common, affordable accesory mount, like Bowens, or Speedo.