1. Will I lose out if I chose a cheap domain registrar compared to one that's popular?
I think it's SAFER to use "http://www.networksolutions.com/" because they are very reliable, and offer great protection both in the WHOIS and transfer departments. Though a contract is a contract ... is a contract. So if you purchase a domain for a period of time, if you are in compliance with the registrar's terms, they are obligated to let you have the domain for the period specified.
2. For a newbie like me, what companies can you recommend for me to register domain names in bulk for cheap or affordable price?
Now if you're looking for cheap then you're best off looking for coupon codes online for various providers like NameCheap or GoDaddy or NetworkSolutions. (There are also third-party resellers like FatCow and MediaTemple to name a few). It all changes day-to-day.
3. I notice that some prices are higher because they offer support and customer service? Aren't those servers not reliable at all?
I'm not sure where you heard that they're not reliable. Maybe hosting-wise. I think it's better to stick with a company offering domains only if you have your own servers, but if you're new to this, maybe a reseller/host is the better option for you. Customer support is a MUST and you should try to avoid any companies with a bad support reputation.
4. I've heard of some domain registrars that they're increasing their prices every renewal? Is that just natural in a business sense for these domain registrars?
Every company does this. They keep prices low on new domains and transfers to sucker you in to using their service, and then charge "normal" rates after it's time to renew. You can avoid this or even get really REALLY good deals, by again, using coupons (30% off orders of $75 or more type of thing) and then buy extended leases, for 5-10 year periods. It will cost a great deal up front, but rather than renew every year for that same time, you could save up to 75% off.
I can say that MediaTemple has VERY good customer care and simple hosting, but they are very expensive for what you get ($20/mo for basic package of domain/hosting). If you're willing to take a few steps out of your comfort zone, I'd recommend using a specialized domain registrar, and then hosting it elsewhere.
And regarding buying in bulk: GoDaddy is the only company I've ever purchased from in bulk, but I'm positive almost all others will provide comparable discounts.