There are a couple of capable UFA LTs - Penn, & Smith from CIN, come to mind.
Ferguson is NOT irreplaceable, not by a long shot and both of those guys will be a significant cap savings.
HYATT™ would go so far as to say BOTH Penn & Smith could be signed for Ferguson's $14M and still leave some cap room to sign another interior lineman worthy of being a backup. (Wisniewski, perhaps.)
As for the QB stockpiling issue, you NEVER stop acquiring and developing QBs, and you spend whatever picks you have to, to keep the pipeline filled.
Some like Petty, HYATT™ believes he is a career backup.
The difference between QBs taken late in Rd 1 and even later in the draft is not huge, but it is definitely a step down from QBs who get drafted in the top half of Rd 1.
The fact that guys like Wilson, Kaepernick, Cousins, & other late-rounders were taken late was much more a failure of the draft talent evaluators being bad at their jobs than it was those QBs somehow overproducing for their draft slot.
Rather than put individual QBs into a draft round, evaluators should group them by tiers.
This year doesn't have a Top-tier like Winston/Mariota, Luck/RGIII or Eli/Ben/Rivers, but all of the top 5 or 6 are still better prospects than anything that would have been labeled as Tier 2 in the past couple of drafts.
Cook is rightly a Tier 2 prospect, but he is also at the very top of that tier and worthy of a mid-to-late Rd 1 pick this year since there are no other Tier 1 candidates - and he is assuredly a better prospect than Petty was.
HYATT™ would have NO trouble turning the team over to Cook as a rookie, but would prefer to see him get 1 or 2 years behind FitzMagic.
Wentz will also probably develop into as really good NFL QB - in about 3 or 4 years.