Ravi,
This question is really broad, so I'll give a few tips:
1. Depending on how many routes you're wanting to receive, you'll need to make sure that you have enough memory to support those routes. You have the options of default route all the way to the complete internet routing table. Obviously you'd need less memory for a default route vs the whole routing table.
2. You'll need to decide on an AS to give you your provider (in the case of using private ASes) vs an internet AS, whereas you'll need to register for one (unless the provider assigns you one).
3. Convergence is not as fast as an igp. Even in the case of ibgp, it's much slower than eigrp or ospf in convergence time.
The most important thing would be to make sure your router/IOS support BGP. If you get a low end router and try to receive the complete routing table, you're going to run into a lot of problems.
HTH,
John
HTH,
John
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