Question about my new all grain set up

So I just finished my mash tun. It's a 5 gallon igloo cooler with a SS braid on the bottom. According to my sparge pal calculator, for 10 lbs of grain I need 3 gallons to mash in, and it says about 5 gallons to sparge. Taking into account absorption and losses, that should give me about 6-7 gallons to boil. I can only boil 6 at the most with my current size pot. Can I skimp on the sparge water and do something like 3-4 gallons? Or maybe lower my mash volume? I'm thinking I need a bigger pot...

By the way, this is for a 5 gallon batch.

Just grabbed one of these to solve that problem for me...

Well, I can boil 6 gallons. With boil off I should get around 5 gallons left over.

So I'm looking for a way to lessen my sparge quantity. I suppose I could do Biab and batch sparge?

Is using top off water a no-no in all grain? Suppose I lessen all water quantities and then top off with a gallon?

Just wondering. New to all grain...

Your good with top off water. Just test your gravity each time before you add any to make sure your not diluting it too much.

Is using less sparge water going to reduce me efficency?

It probably will reduce your efficiency. You could probably do 2.5 gallon mash (at about 1qt/lb) which is pretty thick. It may impact the finished product. but it will let you get all the sparge water.

So if I start with a 6 gallon boil, and half way through I notice my volume is below 5 gallons, can I add more water without harming the final product? Or should I wait until I cool to add the water to be able to check gravity?

Also, what is more important? Mash volume or sparge volume?

I use to have to deal with this a lot before I got a big enough pot. I would just pull the six gallons to boil into the boil pot and whatever was left in the mashtun after the sparge into another pot. Do your boil, and if you are getting too low add some from the other pot. Just make sure you boil for just a little bit to sanitize the wort in the second pot, since it has just been sitting there.