Interested in walking the Camino del Norte in July

@maniparab welcome to the forum. You will find most of the answers to your questions within the Norte pages. https://www.gronze.com/camino-norte is a very useful planning tool.

To walk all the way to Santiago from Bilbao will take 25 - 30 days if your are fit and avoid injury. Budget €25 - 75 per day depending on your inclinations and accommodation standards.

Happy planning

The cost will vary depending on the type of accommodation you use. If you wish to use the albergues (with dormitory style accommodation) then accommodation will be about 10 to 15 euros a night. If you plan on using hotels, then accommodation will be anything from 30 to 100 euros a night.

The Norte is a holiday area, and in July I would expect it would be busy with holiday makers. Its a few years since I walked it, probably better to get more up to date information on whether it is necessary to book ahead.

We are starting from Bilbao in early June. We will book the first night and maybe the second, and then we will take it from there, booking ahead only if we need to. We prefer the alburges to hotels, one advantage is that the public alburges don't take reservations, first come basis. I'll probably post a couple of times when on the way including what the accommodation situation is.
If you are looking at hotels in the peak holiday season you may need to book more ahead. I'd suggest that you not book all of your nights before you start as that locks you into a tight schedule, and doesn't allow for any flexibility if you get injured, walk more or less in a day, stay with friends you make along the way etc.