Cowardly Display

I'm scared. Scared of? The prospect of having to face formal job interviews.
I've only ever been to 2 interviews in my whole life. First was back at the naive age of 18, trying to convince the scholarship board that I am worth them banking a big sum of me for overseas study, and failing miserably at that. 2nd was 2+ years ago, in a 5 min interview, and being slammed by the employer, but thankfully, still managed to secure the offer.
As such, I have practically zero experience at handling interviews. I'm trembling inside now, thinking of having to sell myself to a potential employer.
It's a reversal of roles - from the one being courted, to the one seeking.
About 2.5 months ago, one of my suppliers surprised me with a potential job offer - essentially sales project management position. He's in need of an assistant to help him cope with the projects in the region and having interacted with me (or rather hounded by me for answers), thought I might be suitable. Hence the poaching exercise..
We had 2 rounds of discussion since, nothing formal, just talks about the position, and him trying to sell me the idea. But yesterday night, he called and stated I need to give him a reply - a reply of interest. From which, I will go on to the formal rounds of interviews.. 3 to be exact. With him, with some HR consultant, and other management in the company. That's where the fear comes in...
I know that for my own good, I should say yes and go through the interviews. Gaining experience at interviews can only be good for myself, and have nothing to lose. But I don't know if I am mentally prepared. But I guess I can make myself prepared. I just need to suck it up, and go through with it. Even if I don't get the job in the end, I will benefit from the whole process. I might even convince myself wholeheartedly that this career switch might be right for me..
I guess my fear stems from the fact that I am not 100% convinced of this offer. I've been struggling for past 2 and half months, thinking about this. It's a totally different ball of game from what I know. God knows why my supplier thinks I'm suitable. Just seem ludicrous to me that I turn from the client to the vendor, sitting now on the opposite side of the table, literally. I don't know if I can convince the interviewers that I am the best person for this job, when I can't even convince myself so. Maybe I need to deploy my acting skills.. But one should be honest and be oneself, acting will only make things disastrous. This position is attractive. Glamorous even. Jet-setting about the region. Representing one of the biggest players in the industry, with annual turnover of 1.4 Billion Euros! Wearing smart and chic clothes to meet clients, handling projects worth a few million euros each. This is all so different from my current work!
Oh well.. Guess I will indicate my interest. It's only the right and smart thing to do. From there, I will just have to face the music. Think I need retail therapy again... A round of shopping for interview clothes might just be the antidote to psyche myself up... Haa... Yes.. It's really just an excuse to go shopping...