Definitely lease another plane.
If the routes have business class demand, it will definitely be good to eventually have some seats, since 1 business seat = 3 economy seats for revenue. Depending on the plane, you can often take out 1-3 economy rows and replace them with the same number of business rows. For other planes, the 1st business row requires ripping out 2 econonmy rows. F100 is good that way, standard seating is 21 rows of economy, the first 3 business rows only cost 1 economy row each, so you can go 100/4, 95/8 or 90/12. However, on startup, it's probably better to spend the money on more planes, rather than spend it on new seats. Reconfigure the planes later, once you're up & running.
5 destinations with 2 planes sounds high, better to fill existing routes rather than start new ones. Helps with your competition too, flying twice on one oversupplied route will get you better LF than flying once each on two different oversupplied routes. Better if you can find some empty or near empty ones though, or a route that your competitor flies once daily with a big plane, but you can do 3-4 times with an f100.