If there is no minimum order there is nothing speaking against the 5700°k strips for vegging.
A HLG-240 has up to 280w and is enough for a 4x 2' area. You could use 2 or 3pcs 10gal pots and a SCROG technique or up to 36pcs 1gal pots with cuttings and SOG with almost no vegging.
It's up to you how many plants you can put in in your area. SOG is the fastest technique but requires a 2nd area for mother and/or cuttings. 1-3 huge single plants needs 4-8 weeks of vegging depending on growstyle(hydro/soil) but the slightly better yield can not make up for the difference. In the time you need for 2 SCROG runs you can do three SOG's.
There are three ways to dimm HLG drivers, via resistance(B100k Potentiometer, linear), 1-10v or 10v PWM. The latter is the only solution one could call digital, the other two are analog but it really doesn't matter how you dimm.
The easiest way is a simple rotatable B100k poti+dimmer knob you can find on e3ay/am4zon, a 10pack costs ~3$. Use a multimeter to check their resistance you want the one with 108k or near to that to squeeze out every single watt of the driver.
If you really want something digital you need an aquarium/reef controller(HurricaneX, Storm, StormX but make sure you get the 1-10v extension card(100-150$ incl. 10v extension card).
http://www.stevesleds.com/HurricaneX-LED-Controller_p_237.html
http://www.rapidled.com/storm-sunrise-sunset/
Extension-Board, 0-10V analog dimming
http://www.rapidled.com/10v-analog-converter-for-coralux-storm-controller/
Most of this reef controller only have 5w PWM dimming which is not siutable with HLG-drivers. The more expensive Bluefish controller have build in 10v PWM dimming(200$).
https://www.rapidled.com/bluefish-led-controller/
It's nice to have because you can mimic sun rise/sun set and start with more coolwhite in the morning and finish the day with more warmwhite but it's not so easy to set up for electro noobs.
Pacificlightconcepts has something thats zigbee compatible means it could be use with home automating systems. Controller and HUB is only 65$ and it works out of the box with HLG-drivers. It allows dimming but not to mimic sun rise and such things. But it has an integrated timer and relay to switch the light one and off.
http://www.pacificlightconcepts.com/product-category/diy/wireless-control/
All this dimming solutions are a lot more difficult to realize like dimming via resistance. Simply solder the blue wire to the middle prong and the white one to the left side. Below is a stereo poti one could use for two drivers, you need a single channel poti.
And tell the unbelievers they should google "sun cloark". It's a really efficient and stress-free lighting system and can grow huge plants and impressive yields.