Honestly size means nothing. Its more endurance based
You can be a big guy but have great endurance.
As per the gear for the basic trek, ya I got all that figured out. Its alot of stuff, but well worth it, esp I can still use it during a cold Canadian winter. The main thing is to make sure all the base layer stuff is Merino wool. Even socks and underwear.
And ya as per the price, the 11k is based on the trek itself to base camp, then to go up and reach Camp 1. It becomes very pricey when you climb up. As typical most climbers have there own Sherpa, and then there is all the permits and such. Now if im going to go to Camp 1 yet, I have no idea, its alot of money to drop. But to me its the experience of a life time or could be the end of life hahaha. If its my time to go then its my time to go. Its extremely dangerous going to Camp 1, but no point in worrying about it.
And ya as for taking gear to Kathmandu, you can actually rent alot of stuff in the city, now alot of stuff is fake brand name, but it still does the job.
Well if you ever decide to go, enjoy and be safe