Hey there, ZaramMaldovar!
I'm not a kensai expert, but I did solo no reload one through BG1 with SCS about 8 years ago.
Pick up the Shield Amulet from the merchant at the carnival. That's a limited charge item that will give you a base AC of 4 with a -2 adjustment vs missiles, comparable to unenchanted splint, save the lack of a crushing adjustment.
Be on the lookout for potions of defense, potions of invulnerability and potions of stone form. They will all set your base AC to 0, similar to ankheg plate, but better by 1, and you can still use a magical protection item. The potions of stone form will reduce your dex, cutting into the AC bonus, but that can be offset with potions of mind focusing.
Speaking of potions of mind focusing, whether you're using potions of stone form or not, they're great to keep on hand. I use them with all my characters but they're especially useful for kensais.
If you're fighting a blunt weapon wielder, remember the Girdle of Bluntness. Also, remember that potions of absorption will reducing your AC v crushing by 10, a huge boost against Taurgosz and Drasus, among others.
The Golden Girdle, found on Kirian, is helpful for slashers.
As for ranged fighting, you're on the right track with the Boots of Avoidance and Girdle of Piercing. I'd recommend the Cloak of Displacement from Ulgoth's Beard, too. I, personally, am a Claw of the Kazgaroth fan, but some people are less enamored with it. Weigh the costs and benefits and see whether it makes sense for you.
While Kensai's are often seen as specialized melee fighters, they're also great at range, wielding throwing daggers and axes. My advice would be to fight at range with the Cloak of Displacement + Boots of Avoidance + Girdle of Piercing + Shield Amulet for most battles, in the interest of conserving resources. When you want to fight in melee, use your potions. A basic combo like potion of defense + potion of mind focusing + potion of regeneration + oil of speed will work well against warriors and such. Add in an exceptional strength potion and a potion of heroism if you'd like additional damage output. Against mages and clerics you'll want to layer others in, of course. Read the item descriptions and experiment. Eventually you'll find the brews you need.
That should be enough to get you started. Best of luck with your kensai!
A.