It depends where you will be buying - the transfer tax is higher in some regions than it is in others. In Andalucia it is 8% so 10% should cover that plus legal and notary fees, maybe allow 11 just to be on the safe side. If buying a real "bargain", remember to check the official valor tasación (the catastral value x the municipal multiplier) as if the sale price is lower than that, Hacienda are highly likely to send you a demand for the additional transfer tax which would be due on the higher value.
In some regions you might have to set aside 13/14% of the purchase price.
I wouldn't feel pressured into buying because of rising prices, if I were you, despite what estate agents may tell you. Such prices as there have been have been tiny so far (about 1% in the first quarter of this year nationally, I believe). In some property hotspots they may have risen more but they are few and far between.
Although we didn't rent before buying we did, as I said earlier, know the general area quite well. I think you'd be well advised to at least spend a 2 week holiday (renting a house or apartment rather than staying in a hotel) in the area you're looking at, and spending your time scouting out things like how much everyday things cost in the shops, transport links, ease of parking if you have a car, health centre and hospital facilities nearby, etc., rather than at the beach or eating out all the time. You can have some time off in the evenings to enjoy yourselves, though!