What are some difficulties animals had to overcome to reproduce on land?
The disadvantages you mention have not much to do with reproduction, but with locomotion and oxygen absorption.

Difficulties to reproduce on land are the fact that aquatic egg-producing creatures typically lay soft eggs with porous shells to promote exchange of water and waste products with the surrounding water. Water is essential for growth as a typical creature consists for some 70% of water. Soft-shelled porous eggs when laid on on land dry out very quickly and are prone to predation. 

The main adaptation to reproduce on land instead of water has been the development of the amnion. The amnion is basically a membrane filled with water (the amniotic sac) in which the embryo is immersed during development. Hence, you could argue that the transition to land in terms of embryonic development has never taken place, as the embryos develop in a protected aqueous environment contained within the amnion! The early amniotes laid eggs on land where the embryos develop, while the later ones such as humans carry their embryos/fetuses around. But early as well as late amniotes are characterized by a developing embryo immersed in a watery environment contained in the amnion. Other structures that aided the transition to land were eggs with hard shells, and the allantois. A hard outer shell in amniotes that lay their eggs on land  helps to protect them against drying out, the harsh terrestrial environment and predators. The allantois helps to exchange and store waste products produced by the embryo, a structure not needed when eggs are immersed in water and waste products can diffuse freely through a weak and porous shell.