Particularly in the field of web (contrasted with physical products/live events for example), the need to consider compliance is reduced. If you are providing a good service to users, it is unlikely you will run into issues in terms of consumer complaints.
I would caveat it by suggesting that intellectual property is (obviously) an important area to consider. However, there are online tools for patent searching which will be able to give you an idea of whether your product could be patentable (no patent search even done by a lawyer or patent attorney would be exhaustive in any event).
As to brand protection, trade mark registration in the territory where you are based will be relatively cheap and will give you a degree of leverage if someone else starts up a similarly named service. Although it must be said that the main reason people will copy a name is to piggyback on goodwill which will not be a relevant consideration for most start-ups.
Many actual start-up lawyers will be willing to give a few hours of their time for free or at least should be, to talk with you about your business and highlight any initial concerns and make recommendations to help your business.
If they do provide recommendations, I suggest that if they haven't done already you request a fixed rate for any one particular piece of work. If they can't provide a fixed rate, I suggest you look elsewhere. There are sufficient good lawyers out there to enable you to find one who will be willing to be more flexible on fees than rigidly sticking to an hourly rate.
In terms of tax, I would suggest the above but in relation to an accountant, the basics of corporate taxation are relatively simple and you should be able to find an accountant willing to give you time for free.
On a side note, although it is easy to bash lawyers' fees, if you are a large corporate operating in an area where legal compliance is crucial, an hourly rate of $1000 per hour is a drop in the ocean if it saves you many multiples of that in avoiding costs. Blame shifting in ensuring you have someone that you can sue if they make a mistake can be priceless. But that doesn't mean it's appropriate for start-ups particularly considering monies could be spent better elsewhere.