Well, I am sure you will manage this journey too without any problems divided in to three segments namely
Ahmedabad >> Jaipur >> 675 kms
Jaipur >> Chandigarh >> 500 kms
Chandigarh >> Simla >> 115 kms
In Jaipur depending on the kind of trip I have stayed at different places with different budgets. For a simple overnight stay I would recommend the Fortune Select Metropolitan. This hotel straddles the front portion of a mall that has a CCD or Costa and a nice play area for the kids. Across the road is yet another mall with a McD on the ground floor and a cineplex to boot. The general area is quiet at night but humming with activity during the day as it is very close to the station and straddles the beginning of MI road which is the main shopping area and has various eating options. The hotel itself serves very good cuisine and the two malls also offer various options. Just down the road is another independent shopping complex that houses a subway and a stone's throw away is the ITC Rajputana where I strongly recommend the 'Peshawari' restaurant. The Rajputana also has a 24 hour coffee shop that serves great food and is busy well in to the late hours. In case you stay at the Rajputana do remember that the old wing has very large rooms but overlook the approach to the railway platforms, so a sharp hoot to two is not uncommon. The trick here is to ask for a room no higher than first floor so that the neighbouring buildings block the sounds. The new wing (building perpendicular to the main hotel) has quieter but smaller rooms.
I would recommend my current favourite the Marriott too which offers better standards than the ITC (room wise) at half the price and with an excellent 24 hour restaurant and a speciality Indian restaurant 'Zaika' but then that is across the town close to the airport and a little away from the action. It is a better option for longer stays. Again in the general area of the Marriott our own fellow member 'deky' has his own establishment "Starboard". I have stayed at his place too as have various other Tbhpians and I highly recommend it for an overnight stay. Being a guest house he does not offer meal options in general though I got a fantastic dinner but there are places nearby and the rooms themselves are large and very neat and clean. Being an ex mariner from the hospitality side 'deky' runs a tight ship and the boys there offer excellent service and look after you as one would look after a personal guest at home
What else can i tell you, ok so beyond Udaipur let me list out a few options for food and bio breaks. BTW while @Udaipur do not take the bypass road, instead drive straight in to the city and at Surajpol take the university road to drive to Dabri and rejoin NH8. Till last information as of a 3 odd months back the bypass was in bad shape (has been this way for some years now) and it is easier to go via the city. Time taken is same and so is the distance, besides this gives you an opportunity to go through the market/ hotel area etc. just in case. Now back to beyond Udaipur
1. 135 kilometres beyond Udaipur between Chittaurgarh and Bhilwara you will get BPCL Soniyana (1 km+ from the toll booth on LHS). This houses the apna Dhaba and offers clean loos, well as clean as one can get.
http://catalog.bhilwaraonline.in/Business/ghardhaba
2. In case the need arises to buy something you can leave the NH8 beyond Hamirgarh (marked by a large HP company owned bunk (very large and on your RHS). Approx 8-9 kms. beyond this pump you will see a Black Granite gateway to your RHS saying "Welcome to Bhilwara" Take this turn and going through the gateway 5 kms down on your left hand side you will come to the cleanest hotel in Bhilwara. It's name is Paradise or similar (I will look for the exact name and advise). The area around is barren but don't let that scare you. The same road takes you to the leaner side of Bhilwara rail station with market along side. Keep straight and you will climb a flyover that forks at its crest. The straights/left arm is what you want and a few kms beyond it will bring you back on to NH8. The left arm doubles back and takes you in to Bhilwara town.
The other good thing about this turnoff is that from the point of leaving and rejoining the NH8 it enables you to skip a toll plaza and saves 15kms distance wise.
3. The NH8 after Nasirabad culminates in to the Kishangarh Jaipur highway. Take the ramp up to join the Expressway. In case you need a break go along side the ramp towards Kishangarh. Under the ramp take a left and about a half kilometre down the road is the hotel Heritage to your left. A decent place for a break.
4. Back on the expressway halfway through you will cross Dudu which has yet another BPCL COCO with an 'Apna Ghar' however here drive a few more kilometres (35) to BAGRU and you will come to Hotel Highway king, yet another decent option for a quick halt. In fact between jaipur and Delhi too the same group has two more establishments at Shahpur and then at Behror.
http://hotelhighwayking.com
5. Beyond Dilli the one decent stop is the Haveli complex at Murthal
http://haveliheritage.net/murthal/
6. Also at Murthal you will come across various dhabas on your LHS as soon as you come down the flyover. These are namely "Pehelwan" "Gulshan" "Sukhdev" "Ahuja" and a few more.
Now these dhabas are open 24 hours and serve only veg food, their speciality being "PARANTHAS" with white butter. They also offer cleanish facilities, the trick is to eat here and then use the facilities at Haveli down the road. People from Dilli drive out on lazy Sunday noons for an extended brunch of the traditional taste. The recommended one being 'Aloo Pyaaz (onion) parantha". I prefer Gulshan as his parking lot is bricked up and he offers inside sitting option in case the weather is unfavourable (too cold or hot).
I have posted what all I could remember off hand. Let me know if you need any additional information