This is what I read from Austrian Embassy in Washington website
If you intend to stay in Austria for more than 90 but less than 180 days as a tourist, student, on a business trip, to visit friends or relatives, or you intend to take up short-term employment (less than 6 months) AND you are neither an EU nor an EFTA citizen, you need a national Austrian visitor visa (Visa D).
**The Visa D entitles you to stay up to 90 days within 180 days in the other Schengen countries. A Visa D will allow you to work temporarily under clearly specified circumstances (e.g. if you are an artist or entertainer on a short-term employment/contract, see more information: www.migration.gv.at) in Austria. It is not a work permit per se and, as such, does not allow you to take up any employment you like. Please note that you need the visa D to legally take up your temporary employment (as outlined above) even if you are allowed to enter Austria without a visa and your stay does not exceed three months.
Then, from the provided link, I read this:
**Self-employed person* (if the Foreign citizen has contracted to perform certain services and the contract covers a period of more than six months; AMS may be involved)*
What I think this covers are activities like IT free-lance jobs, consulting gigs and the likes. You need to check with AMS whether pet sitting is an occupation that is covered by the unspecified short-term employment exception for D visas.
As for accommodation, if you don't have hotels reserved, you will need a suitable residence, as outlined on their website listing the requirements:
The following requirements must be fulfilled for any residence title to be granted:
**Adequate means of subsistence: The applicant must have fixed and regular own income enabling him/her to cover his/her living costs without resorting to welfare aid from local authorities. When applying the regular monthly income must be equal to the amount of the standard rates of the General Social Insurance Act (ASVG).
> For singles: €814.82
> For couples: €1,221.68
> For each child additionally €125.72
Health Insurance Coverage: The applicant must have health insurance coverage providing benefits in Austria.
Adequate accommodation according to local standards: The applicant must provide evidence of a legal title to an accommodation (e.g. by providing a lease contract), considered adequate for his/her family size according to local standards.
I think you can get over employment requirements if you have substantial demonstrable financial savings, especially if you are older than 50 or so. However, I think you will have problems if you present your application without accommodation settled in. There is no such thing as a "I'm going to wing it, arrive and decide what to do" visa.