In terms of healing, I recommend using Hit Dice (Short Rest) or a healing potion over Spell Slots.  Personally, Pavel could use a SR to recover his Action Surge and Fiery Shackles and then he could/would heal with a Short Rest.<br/><br/>In terms of environmental conditions, there are a few.  You can get +2 AC for half-cover, +5 AC for 3/4 cover, and if prone disadvantage or ranged attacks, but advantage on melee attacks. I have not seen a lot of DMs and a players, allow/use the environmental adjustments.<br/><br/>Flanking is an optional rule, it tends to favor the party with greater numbers or at least greater numbers willing to get into melee. For example, a party against one large monster favors the party, while a horde of monster vs. party favors the horde. Also flanking tends to deprecate monsters (e.g. wolves) and characters (e.g., Wolf Path of Totem) that can create advantage through things like Pact Tactics.