I've also been dealing with achilles tendonitis (plus a heel spur!) over the past year prior to setting out on my own Camino this May. I feel your pain, literally and figuratively.
As I'm sure you're aware and as others have mentioned here, achilles tendonitis is difficult to treat, especially quickly. Physical therapy exercises and KT tape were both recommended but neither did much for me.
My podiatrist recommended the use of 1/4"/6 mm heel lifts under the inserts of my Altra shoes (apparently "zero drop" shoes can contribute to achilles issues), which helped ease my tendonitis considerably over a period of several months.
And although it's a contentious threatment, I also received a cortisone shot a few months ago which alleviated my discomfort completely. I plan to get another one a week or two before my walk. (There is evidence that these shots can potentially damage the tendon over time, so of course talk to your podiatrist in detail about it. For me, it's practically been a miracle cure.)
As for shoe tightness and pain on the top/sides of feet, I experienced all of the above when breaking in the shoes I had been planning to wear on my Camino. I was almost ready to give up on them before I tried switching to a "no tie" lacing system with elastic shoelaces. The system not only stabilizes the foot inside a shoe as good or better than conventional lacing does, but does not cause undue pressure across the tops of the feet. It also completely alleviated my pain and feeling that my shoes were too tight/narrow. (Plus, no more untied laces - and the system makes adjusting lacing tightness much easier, which is a boon for dealing with feet swelling during a long walk.)
Over 9 million pairs sold. Turn any shoe into a slip-on with Lock Laces. Cheapest place to buy online. For runners, triathletes, and those looking to never tie their shoes again.
They're inexpensive enough to be worth a try.
LockLaces are one well known brand name, but there are a few others.
And finally (and speaking of laces in general) the website below has been an invaluable resource for me in finding a lacing system to alleviate many common foot/shoe problems including heel slippage, metatarsal pain, tendonitis, etc. Turns out that proper lacing techniques (and possibly trying out different ones from the one you usually use) are a lot more important than most people think!
An extensive selection of shoe lacing tutorials, including traditional, decorative, functional and military methods.
Standard disclaimers apply: I am not a doctor, your mileage may vary, talk to your podiatrist first, etc.
Wishing you all the best on your journey ahead!