I have been through this process myself and would urge you to carefully read the below link so that you are aware of the requirements (not just the ones listed on NPRA website). Detailed FAQ included as well. Scroll down towards the end of the post for the property purchase and self sponsorship visa process.
https://www.expat.com/forum/viewtopic.php?id=750635
1) It can vary. Some nationalities never get it. For most people who have spent time in Bahrain, it will range between 1.5 to 3 months. For others, it can take longer. It really depends - you need to understand that they actually do a super detailed clearance with agencies like Interpol, terrorism watch lists etc etc., (try and get a look at your security clearance report when you are in notary office for property purchase and if the guy is friendly - they have it as part of the file when you go to execute property transaction) so the availability of past data in your country of origin also plays a lot into it - especially if you left decades ago when the records of the time were manual (one of the key reasons why a lot of people from Yemen who have lived in the ME all their lives don't clear this - missing records or mismatches in official files in Yemen)
2) Already answered on the FAQ - extract follows:
1) If property is in two names, do both parties or one only become eligible for the visa? - Not many people are clear on this but each person's share must be 50K BHD, to be eligible for a visa. If the share works out to be less than 50K then no one is eligible for a visa. A lot of people will tell you that husband and wife on a 50K property will get a visa - also a lot say no. The answer is yes (but only for husband and wife) and it is possible if you have an attested marriage certificate, both are equal shareholders in the property, electricity bill is in husband's name and the husband applies for the visa & then sponsors wife as dependent (Same situation as me - visa was approved). BUT this is allowed only in the case of a husband and wife relationship; all other family relationships are subject to the same rule of 50K per person per visa
3) No medical
4) You need a basic medical insurance policy which covers hospitalization. Shop around - it usually costs anywhere from 200 to 400 BD a year for family. Also practically speaking, all they need is photocopy / scan of the medical insurance cards
