You could save yourself the often considerable expense of a Lonely Planet guide by getting one at your usual Library. You'll also find it handy to have it ready 'out there'. Subscribe to Lonely Planet updates to get the most recent addendums to whichever guide you have.

I travelled with World Expeditions in 2004 (10 day Kathmandu Explorer, similar to the their current Nepal Special ) and this is probably the best way to go leaving logistics, administration, passports etc and accommodation to a business well-versed familiar with the area.