Unless you are on smooth pavement, this type of device becomes difficult:
1) Sand/gravel/FOD entrainment is a serious problem, and one of the reasons the original Chaparral 2J was banned. Anyone at GRM $2007 challenge saw the Cheaparral blow sand 15-20 feet in the air. The cast aluminum fan blades showed noticeable abrasion, with sand all over the interior, and the glass windshield was pitted.One of the junk science Discovery channel shows did an example of a vacuum system test on a dirt road, intended for preventing logging truck rollovers. It worked, but was a huge dustball.
2) The side skirts coming off the ground is not a big deal. Its a more gradual loss of suction than expected. But the difference in static pressure between 10 & 15mm gap height is significant. Even 600-1,000 lbf of downforce on a street car is worth up to 40% higher lateral acceleration. Much bigger differnce than street tires to race tires. Hence 2J2 won FTD on its first run of day, with cold race tires and a dirty track. I assume you can make a quick simulation of 1.14g's for race tires vs 1.4 g's with sucker system and figure out your lap time difference. If you are using slicks, the difference is proportional. And light weight becomes ever more important, as it maximizes the advantage of downforce.
3) Noise is a real problem. Well over 100dB. Ear plugs, helmet, and 1/2" lexan safety plate make it tolerable short term, but not safe long term. Hearing damage is a real problem, and happens with no notice. Even if personal safety isn't a problem, most tracks/courses have rules, to prevent neighbors from shutting them down. Not something that could be run on the street. Much of the noise is from a 2 stroke engine running wide open, but even the fans are 100dB or so.
4)Jim Hall did it right with the articulated skirts on the 2J. 2J2 did not, for simplicity of build. Any articulated skirt system needs dampening, as they can bounce a lot. His cars are on display in Texas.
5)Wings are much more efficient and effective at track speeds. The people saying powered undertrays are less effective than venturis are wrong of course. Any race designer would love to have a more effective means of powering the undertray than simple venturis, at least at low speeds (all aero is easier at high speeds). And the fan powered systems do not generate aero drag. However, the engines for the fans are gasoline and hp hungry. Figure ~40hp continuous duty for even a basic system. And small engines generally have higher bsfc at full load, high rpm. If you drive it off the engine, then you have a huge problem with fan speed varying with engine speed, and generally being slow in mid corner where you want the fan maxed out. Refilling the gas tank every 8 minutes of run time gets old fast.
6) a second engine is a reliability and safety problem. More things to go wrong. And a second fuel system that really should have a fuel cell. Or its own fuel pump. The weight is not that much of a problem, maybe 200#. The cost is debatable, but will depend largely on the fan selection and sourcing, which in turn depends on the skirt design choices.
7) center of pressure of skirt system should be balanced with the cm and relative roll stiffness of the axles to prevent unpredictable understeer/oversteer. This may be a problem, if you are rallying on dirt/gravel roads, where a rally cornering manuever of deliberately fishtailing is the fast line. Downforce might prevent this, if wheel torque is insufficient.
You should also look at what Cornell did on a FSAE car. It would be great fun to make a streetable sucker car, but the problem would be where to use it. In almost any form of racing, the sucker systems are good for 10% improvement in lap times. (Wings are even more effective, at high speeds). Which means either everyone is compelled to run them to be competitive, or the rules ban all such devices.
That should be enough to get you thinking.