Every point in SPD increses the SPD of your hero’s units by 0.02. To get your Human archers to 5.89 SPD, you’d need a hero with 50 SPD. I don’t know if it’ll be enough to have equal SPD to strike first – to be sure your hero should have atleast 51 SPD.
Everytime you finish all fights in any dungeon your HP will be restored to 100%. Everytime you die your HP will be “restored” to 50%.
To finish an easy dungeon is the usual way to heal yourself between dungeons.
for Lvl’s till ~40 i suggest the dungeon with 4 Mudwamps and 1 Toxic Thornhoof in West Hills. 1 single fight, quickly done for around 150 silver and 112exp.