maximum file size website

Question 1

You shouldn't worry about the size of your website (especially since you know your target audience) if the user experience doesn't suffer. However, you should optimize everything you can without sacrificing the design. Google's Page Speed might help you a lot. They even have the total size calculator you wanted. There are tons of similar tools available online as well.

Also, read this about last year's website size trends: http://www.theglobeandmail.com/technology/tech-news/bloated-web-pages-costly-for-smartphone-users/article9355125/

According to the website HTTP Archive, which regularly studies the top 10,000 most-visited sites online, the average web page now weighs in at about 1.3 megabytes, up about 35 per cent in the last year.

UPDATE

Inspired by @pwdst's comments, I'd like to add that if you want support for mobiles, tablets, etc... there's no need to sacrifice the look of the main site - you can use media queries and practically serve a different presenation to those users. Of course, you can go even further and make a different website for them (usually a subdomain).

Question 2

If you use dev tools, for example in Chrome, you can see the number of requests and total transferred data under the "Network" tab. To accurately replicate the experience of your users, you should do this with an empty cache - "Incognito" or "Private" tabs can be a great way to do this in most browsers. It's also worth remembering that the experience when testing locally will be drastically different from that when the effects of latency and upstream bandwidth come into play.

Be extremely careful about assumptions regarding users if you want to maintain usability. "Good enough" is extremely contextual, it may be "good enough" for a user on a desktop, laptop or premium tablet on a solid DSL connection - but anything but on a Edge or 3G connection on a phone. Wherever possible assumptions should be backed up by analysis of user agent strings from server logs, or from analytics software such as Google Analytics. It's also worth remembering that you may have relatively few mobile or tablet requests, not because mobile or tablet users don't want to visit the website - or choose to visit using another device, but because it is difficult, slow or even impossible to use on their device of choice. This case study from an engineer at YouTube illustrates how customers were being completely excluded from the site.

In general the page should be as small as possible, and you may want to look at lazy loading in addition to optimisations, which will help initial rendering time - in fairness though your estimated size is not much larger than the internet archive average page weight of 1681kB as at January 15th this year. Don't forget that other resources can also use a lot of space - JavaScript makes up 274kB of that average - and it's not clear if you have factored that into your estimate. Aggressive use of caching will help return visitors and minimise the data transfer required in these circumstances.

I always try to consider if you can justify the page weight cost against functionality. What is the objective of visitors to your site? Does the added functionality or imagery help this sufficiently to justify the performance cost. Many performance orientated developers are now actively setting a page weight budget but this is harder for single page apps where you cannot be as granular with resources.

Question 3

I would recommend using Image Pre-loading which can help your page loading times, even when its large.