We try to keep in mind that the "borei pri ha’adama" we say on the karpas will also be for the maror. Is there not a problem, however, of too much time passing, since we won’t eat the maror until hours after the karpas? Would it be permissible/desireable to continue nibbling on karpas every hour or so during the magid, so that not too much time will have passed by the time we get to maror?

Karpas on Seder night should be eaten less than Kazait [MB 475:26] so you don’t enter the question of Bracha Achrona after it. Maror is eaten after Hamotzi and strictly speaking does not require Boreh Pri Haadama, however since there are opinions it does require a Bracha we have it in mind when we eat the Karpas [ibid 56]. In any case the Haggada does not separate the two. [for more details see Mikraei Kodesh pp. 180-195]