I actually do not see the point of bringing your tablet without a sim slot just to apply for a plan. You may apply for a plan anytime... with or without your tablet.
You have a choice of whether to get a post paid plan if you plan to stay in the Philippines for at least a year or, opt for a prepaid plan if your stay would only be for a short time. There are devices which could serve as wireless modem/router and the people at the Globe Store would be able to suggest one that would suit your needs and budget.
Yes, you can apply for a plan.
I think you can avail plan with pocket wifis (if you want on-the-go internet) or you can ask Globe Store for a Sim Card plan only and insert it on your phone. Then, activate your personal hotspot. Now, you can use internet both on your phone and tablet!
Yes. You can apply for a plan with or without the tablet. You better check the latest deals of Globe! There are also pocket wifi's available. Better grab the best deal for you.