It's very hard for a large corp to get a high-sec POS due to standing. The main options are usually to form a new corp with a single member of the appropriate standing and once the tower is anchored, everyone joins the corp (or the corp joins the alliance).

As for wardecs, anchor a number of small and medium sized guns (no capitals in high-sec means large guns are useless) at different point outside the bubble. Add generous helpings of web, neut, scram and ECM batteries. Online them (or some of them, always best to have more then less) if a war dec is made. You will have to offline/evac the modules that make you money to have available power grid / cpu to online most of the defenses.

Further defensive considerations:

Any missile-based weapons are completely worthless. Many reasons, but mostly they are completely unbonused and require CPU to run, so they fail if tower is reinforced.

Make sure you have some strontium if you don't plan on taking tower down in case of war.

It takes a really motivated opponent to take down a tower without carriers or dreads.

In addition to normal fuel requirements, you need a corp to faction standing of at least 10*system security (5 for 0.5, 6 for 0.6, etc...) to anchor the POS and you need a starbase charter every hour to keep it online (these are available through LP stores and sell for around 500k per).

Unless you are wardecced, CONCORD will object to people shooting your POS. It is not uncommon for hisec POSes to have no defenses at all and just be taken down in the 24 hours before a war goes active. Without the need to fit defenses, you can probably get away with a small tower which will substantially reduce your fuel costs.