Hi,
About your project:
I can make the multistore. You can choose a theme from themeforest.com. Website speed depends on both website content and server performance. I work on both. Please see my top skill on my profile, I have many experience on magento. Besides I worked outside freelancer a lot.
About my magento knowledge and experience (please read if you need):
I have 8 years experience in magento. I worked mostly outside marketplaces but still I have some work on [login to view URL] and [login to view URL] with excellent feedbacks. Please see my upwork prilfe [login to view URL] and fiverr profile [login to view URL]
I use high neat and clean coding, most optmized coding, search engine friendly coding, systematic coding and so my sites are high fast to load (about 0-3 seconds) and high search engine friendly. My site are easy to upgrade later.
I work myself and so work quality will be high. If a company works then they will use programmers of different experience and so coding quality won't be high.
I do a lot of work to make site highest possible faster to load both on server and website sides. Very few programmers can use these. I also have strong knowledge on SEO.
I also made a lot of magento extensions which require highest level knowledge on magento.
Regards
Subir